diff --git a/Session/Calls/CallVC.swift b/Session/Calls/CallVC.swift
index ed837b7bd..d54af1878 100644
--- a/Session/Calls/CallVC.swift
+++ b/Session/Calls/CallVC.swift
@@ -165,7 +165,7 @@ final class CallVC : UIViewController, WebRTCSessionDelegate {
     init(for sessionID: String, mode: Mode) {
         self.sessionID = sessionID
         self.mode = mode
-        self.webRTCSession = WebRTCSession.current ?? WebRTCSession(for: sessionID)
+        self.webRTCSession = WebRTCSession.current ?? WebRTCSession(for: sessionID, with: UUID().uuidString)
         super.init(nibName: nil, bundle: nil)
         self.webRTCSession.delegate = self
     }
@@ -187,7 +187,9 @@ final class CallVC : UIViewController, WebRTCSessionDelegate {
         if case .offer = mode {
             callInfoLabel.text = "Ringing..."
             Storage.write { transaction in
-                self.webRTCSession.sendOffer(to: self.sessionID, using: transaction).retainUntilComplete()
+                self.webRTCSession.sendPreOffer(to: self.sessionID, using: transaction).done {
+                    self.webRTCSession.sendOffer(to: self.sessionID, using: transaction).retainUntilComplete()
+                }
             }
             answerButton.isHidden = true
         }
diff --git a/SessionMessagingKit/Calls/WebRTCSession.swift b/SessionMessagingKit/Calls/WebRTCSession.swift
index 27996b1b4..b801dd825 100644
--- a/SessionMessagingKit/Calls/WebRTCSession.swift
+++ b/SessionMessagingKit/Calls/WebRTCSession.swift
@@ -11,6 +11,7 @@ public protocol WebRTCSessionDelegate : AnyObject {
 public final class WebRTCSession : NSObject, RTCPeerConnectionDelegate {
     public weak var delegate: WebRTCSessionDelegate?
     private let contactSessionID: String
+    private let uuid: String
     private var queuedICECandidates: [RTCIceCandidate] = []
     private var iceCandidateSendTimer: Timer?
     
@@ -88,8 +89,9 @@ public final class WebRTCSession : NSObject, RTCPeerConnectionDelegate {
     // MARK: Initialization
     public static var current: WebRTCSession?
     
-    public init(for contactSessionID: String) {
+    public init(for contactSessionID: String, with uuid: String) {
         self.contactSessionID = contactSessionID
+        self.uuid = uuid
         super.init()
         let mediaStreamTrackIDS = ["ARDAMS"]
         createDataChannel()
@@ -100,6 +102,24 @@ public final class WebRTCSession : NSObject, RTCPeerConnectionDelegate {
     }
     
     // MARK: Signaling
+    public func sendPreOffer(to sessionID: String, using transaction: YapDatabaseReadWriteTransaction) -> Promise<Void> {
+        print("[Calls] Sending pre-offer message.")
+        guard let thread = TSContactThread.fetch(for: sessionID, using: transaction) else { return Promise(error: Error.noThread) }
+        let (promise, seal) = Promise<Void>.pending()
+        DispatchQueue.main.async {
+            let message = CallMessage()
+            message.uuid = self.uuid
+            message.kind = .preOffer
+            MessageSender.sendNonDurably(message, in: thread, using: transaction).done2 {
+                print("[Calls] Pre-offer message has been sent.")
+                seal.fulfill(())
+            }.catch2 { error in
+                seal.reject(error)
+            }
+        }
+        return promise
+    }
+    
     public func sendOffer(to sessionID: String, using transaction: YapDatabaseReadWriteTransaction) -> Promise<Void> {
         print("[Calls] Sending offer message.")
         guard let thread = TSContactThread.fetch(for: sessionID, using: transaction) else { return Promise(error: Error.noThread) }
@@ -117,6 +137,7 @@ public final class WebRTCSession : NSObject, RTCPeerConnectionDelegate {
                 }
                 DispatchQueue.main.async {
                     let message = CallMessage()
+                    message.uuid = self.uuid
                     message.kind = .offer
                     message.sdps = [ sdp.sdp ]
                     let tsMessage = TSOutgoingMessage.from(message, associatedWith: thread)
diff --git a/SessionMessagingKit/Messages/Control Messages/CallMessage.swift b/SessionMessagingKit/Messages/Control Messages/CallMessage.swift
index 19455a24f..cd3609991 100644
--- a/SessionMessagingKit/Messages/Control Messages/CallMessage.swift	
+++ b/SessionMessagingKit/Messages/Control Messages/CallMessage.swift	
@@ -3,6 +3,7 @@ import WebRTC
 /// See https://developer.mozilla.org/en-US/docs/Web/API/RTCSessionDescription for more information.
 @objc(SNCallMessage)
 public final class CallMessage : ControlMessage {
+    public var uuid: String?
     public var kind: Kind?
     /// See https://developer.mozilla.org/en-US/docs/Glossary/SDP for more information.
     public var sdps: [String]?
@@ -13,6 +14,7 @@ public final class CallMessage : ControlMessage {
     
     // MARK: Kind
     public enum Kind : Codable, CustomStringConvertible {
+        case preOffer
         case offer
         case answer
         case provisionalAnswer
@@ -21,6 +23,7 @@ public final class CallMessage : ControlMessage {
         
         public var description: String {
             switch self {
+            case .preOffer: return "preOffer"
             case .offer: return "offer"
             case .answer: return "answer"
             case .provisionalAnswer: return "provisionalAnswer"
@@ -33,8 +36,9 @@ public final class CallMessage : ControlMessage {
     // MARK: Initialization
     public override init() { super.init() }
     
-    internal init(kind: Kind, sdps: [String]) {
+    internal init(uuid: String, kind: Kind, sdps: [String]) {
         super.init()
+        self.uuid = uuid
         self.kind = kind
         self.sdps = sdps
     }
@@ -42,7 +46,7 @@ public final class CallMessage : ControlMessage {
     // MARK: Validation
     public override var isValid: Bool {
         guard super.isValid else { return false }
-        return kind != nil
+        return kind != nil && uuid != nil
     }
     
     // MARK: Coding
@@ -50,6 +54,7 @@ public final class CallMessage : ControlMessage {
         super.init(coder: coder)
         guard let rawKind = coder.decodeObject(forKey: "kind") as! String? else { return nil }
         switch rawKind {
+        case "preOffer": kind = .preOffer
         case "offer": kind = .offer
         case "answer": kind = .answer
         case "provisionalAnswer": kind = .provisionalAnswer
@@ -61,11 +66,13 @@ public final class CallMessage : ControlMessage {
         default: preconditionFailure()
         }
         if let sdps = coder.decodeObject(forKey: "sdps") as! [String]? { self.sdps = sdps }
+        if let uuid = coder.decodeObject(forKey: "uuid") as! String? { self.uuid = uuid }
     }
 
     public override func encode(with coder: NSCoder) {
         super.encode(with: coder)
         switch kind {
+        case .preOffer: coder.encode("preOffer", forKey: "kind")
         case .offer: coder.encode("offer", forKey: "kind")
         case .answer: coder.encode("answer", forKey: "kind")
         case .provisionalAnswer: coder.encode("provisionalAnswer", forKey: "kind")
@@ -77,6 +84,7 @@ public final class CallMessage : ControlMessage {
         default: preconditionFailure()
         }
         coder.encode(sdps, forKey: "sdps")
+        coder.encode(uuid, forKey: "uuid")
     }
     
     // MARK: Proto Conversion
@@ -84,6 +92,7 @@ public final class CallMessage : ControlMessage {
         guard let callMessageProto = proto.callMessage else { return nil }
         let kind: Kind
         switch callMessageProto.type {
+        case .preOffer: kind = .preOffer
         case .offer: kind = .offer
         case .answer: kind = .answer
         case .provisionalAnswer: kind = .provisionalAnswer
@@ -94,23 +103,25 @@ public final class CallMessage : ControlMessage {
         case .endCall: kind = .endCall
         }
         let sdps = callMessageProto.sdps
-        return CallMessage(kind: kind, sdps: sdps)
+        let uuid = callMessageProto.uuid
+        return CallMessage(uuid: uuid, kind: kind, sdps: sdps)
     }
 
     public override func toProto(using transaction: YapDatabaseReadWriteTransaction) -> SNProtoContent? {
-        guard let kind = kind else {
+        guard let kind = kind, let uuid = uuid else {
             SNLog("Couldn't construct call message proto from: \(self).")
             return nil
         }
         let type: SNProtoCallMessage.SNProtoCallMessageType
         switch kind {
+        case .preOffer: type = .preOffer
         case .offer: type = .offer
         case .answer: type = .answer
         case .provisionalAnswer: type = .provisionalAnswer
         case .iceCandidates(_, _): type = .iceCandidates
         case .endCall: type = .endCall
         }
-        let callMessageProto = SNProtoCallMessage.builder(type: type)
+        let callMessageProto = SNProtoCallMessage.builder(type: type, uuid: uuid)
         if let sdps = sdps, !sdps.isEmpty {
             callMessageProto.setSdps(sdps)
         }
@@ -132,6 +143,7 @@ public final class CallMessage : ControlMessage {
     public override var description: String {
         """
         CallMessage(
+            uuid: \(uuid ?? "null"),
             kind: \(kind?.description ?? "null"),
             sdps: \(sdps?.description ?? "null")
         )
diff --git a/SessionMessagingKit/Protos/Generated/SNProto.swift b/SessionMessagingKit/Protos/Generated/SNProto.swift
index dae62350a..e4263501a 100644
--- a/SessionMessagingKit/Protos/Generated/SNProto.swift
+++ b/SessionMessagingKit/Protos/Generated/SNProto.swift
@@ -658,6 +658,7 @@ extension SNProtoContent.SNProtoContentBuilder {
         case provisionalAnswer = 3
         case iceCandidates = 4
         case endCall = 5
+        case preOffer = 6
     }
 
     private class func SNProtoCallMessageTypeWrap(_ value: SessionProtos_CallMessage.TypeEnum) -> SNProtoCallMessageType {
@@ -667,6 +668,7 @@ extension SNProtoContent.SNProtoContentBuilder {
         case .provisionalAnswer: return .provisionalAnswer
         case .iceCandidates: return .iceCandidates
         case .endCall: return .endCall
+        case .preOffer: return .preOffer
         }
     }
 
@@ -677,18 +679,19 @@ extension SNProtoContent.SNProtoContentBuilder {
         case .provisionalAnswer: return .provisionalAnswer
         case .iceCandidates: return .iceCandidates
         case .endCall: return .endCall
+        case .preOffer: return .preOffer
         }
     }
 
     // MARK: - SNProtoCallMessageBuilder
 
-    @objc public class func builder(type: SNProtoCallMessageType) -> SNProtoCallMessageBuilder {
-        return SNProtoCallMessageBuilder(type: type)
+    @objc public class func builder(type: SNProtoCallMessageType, uuid: String) -> SNProtoCallMessageBuilder {
+        return SNProtoCallMessageBuilder(type: type, uuid: uuid)
     }
 
     // asBuilder() constructs a builder that reflects the proto's contents.
     @objc public func asBuilder() -> SNProtoCallMessageBuilder {
-        let builder = SNProtoCallMessageBuilder(type: type)
+        let builder = SNProtoCallMessageBuilder(type: type, uuid: uuid)
         builder.setSdps(sdps)
         builder.setSdpMlineIndexes(sdpMlineIndexes)
         builder.setSdpMids(sdpMids)
@@ -701,10 +704,11 @@ extension SNProtoContent.SNProtoContentBuilder {
 
         @objc fileprivate override init() {}
 
-        @objc fileprivate init(type: SNProtoCallMessageType) {
+        @objc fileprivate init(type: SNProtoCallMessageType, uuid: String) {
             super.init()
 
             setType(type)
+            setUuid(uuid)
         }
 
         @objc public func setType(_ valueParam: SNProtoCallMessageType) {
@@ -741,6 +745,10 @@ extension SNProtoContent.SNProtoContentBuilder {
             proto.sdpMids = wrappedItems
         }
 
+        @objc public func setUuid(_ valueParam: String) {
+            proto.uuid = valueParam
+        }
+
         @objc public func build() throws -> SNProtoCallMessage {
             return try SNProtoCallMessage.parseProto(proto)
         }
@@ -754,6 +762,8 @@ extension SNProtoContent.SNProtoContentBuilder {
 
     @objc public let type: SNProtoCallMessageType
 
+    @objc public let uuid: String
+
     @objc public var sdps: [String] {
         return proto.sdps
     }
@@ -767,9 +777,11 @@ extension SNProtoContent.SNProtoContentBuilder {
     }
 
     private init(proto: SessionProtos_CallMessage,
-                 type: SNProtoCallMessageType) {
+                 type: SNProtoCallMessageType,
+                 uuid: String) {
         self.proto = proto
         self.type = type
+        self.uuid = uuid
     }
 
     @objc
@@ -788,12 +800,18 @@ extension SNProtoContent.SNProtoContentBuilder {
         }
         let type = SNProtoCallMessageTypeWrap(proto.type)
 
+        guard proto.hasUuid else {
+            throw SNProtoError.invalidProtobuf(description: "\(logTag) missing required field: uuid")
+        }
+        let uuid = proto.uuid
+
         // MARK: - Begin Validation Logic for SNProtoCallMessage -
 
         // MARK: - End Validation Logic for SNProtoCallMessage -
 
         let result = SNProtoCallMessage(proto: proto,
-                                        type: type)
+                                        type: type,
+                                        uuid: uuid)
         return result
     }
 
diff --git a/SessionMessagingKit/Protos/Generated/SessionProtos.pb.swift b/SessionMessagingKit/Protos/Generated/SessionProtos.pb.swift
index 7b4894f60..b3b69166d 100644
--- a/SessionMessagingKit/Protos/Generated/SessionProtos.pb.swift
+++ b/SessionMessagingKit/Protos/Generated/SessionProtos.pb.swift
@@ -311,7 +311,7 @@ struct SessionProtos_CallMessage {
 
   /// @required
   var type: SessionProtos_CallMessage.TypeEnum {
-    get {return _type ?? .offer}
+    get {return _type ?? .preOffer}
     set {_type = newValue}
   }
   /// Returns true if `type` has been explicitly set.
@@ -325,10 +325,21 @@ struct SessionProtos_CallMessage {
 
   var sdpMids: [String] = []
 
+  /// @required
+  var uuid: String {
+    get {return _uuid ?? String()}
+    set {_uuid = newValue}
+  }
+  /// Returns true if `uuid` has been explicitly set.
+  var hasUuid: Bool {return self._uuid != nil}
+  /// Clears the value of `uuid`. Subsequent reads from it will return its default value.
+  mutating func clearUuid() {self._uuid = nil}
+
   var unknownFields = SwiftProtobuf.UnknownStorage()
 
   enum TypeEnum: SwiftProtobuf.Enum {
     typealias RawValue = Int
+    case preOffer // = 6
     case offer // = 1
     case answer // = 2
     case provisionalAnswer // = 3
@@ -336,7 +347,7 @@ struct SessionProtos_CallMessage {
     case endCall // = 5
 
     init() {
-      self = .offer
+      self = .preOffer
     }
 
     init?(rawValue: Int) {
@@ -346,6 +357,7 @@ struct SessionProtos_CallMessage {
       case 3: self = .provisionalAnswer
       case 4: self = .iceCandidates
       case 5: self = .endCall
+      case 6: self = .preOffer
       default: return nil
       }
     }
@@ -357,6 +369,7 @@ struct SessionProtos_CallMessage {
       case .provisionalAnswer: return 3
       case .iceCandidates: return 4
       case .endCall: return 5
+      case .preOffer: return 6
       }
     }
 
@@ -365,6 +378,7 @@ struct SessionProtos_CallMessage {
   init() {}
 
   fileprivate var _type: SessionProtos_CallMessage.TypeEnum? = nil
+  fileprivate var _uuid: String? = nil
 }
 
 #if swift(>=4.2)
@@ -1798,10 +1812,12 @@ extension SessionProtos_CallMessage: SwiftProtobuf.Message, SwiftProtobuf._Messa
     2: .same(proto: "sdps"),
     3: .same(proto: "sdpMLineIndexes"),
     4: .same(proto: "sdpMids"),
+    5: .same(proto: "uuid"),
   ]
 
   public var isInitialized: Bool {
     if self._type == nil {return false}
+    if self._uuid == nil {return false}
     return true
   }
 
@@ -1815,6 +1831,7 @@ extension SessionProtos_CallMessage: SwiftProtobuf.Message, SwiftProtobuf._Messa
       case 2: try { try decoder.decodeRepeatedStringField(value: &self.sdps) }()
       case 3: try { try decoder.decodeRepeatedUInt32Field(value: &self.sdpMlineIndexes) }()
       case 4: try { try decoder.decodeRepeatedStringField(value: &self.sdpMids) }()
+      case 5: try { try decoder.decodeSingularStringField(value: &self._uuid) }()
       default: break
       }
     }
@@ -1833,6 +1850,9 @@ extension SessionProtos_CallMessage: SwiftProtobuf.Message, SwiftProtobuf._Messa
     if !self.sdpMids.isEmpty {
       try visitor.visitRepeatedStringField(value: self.sdpMids, fieldNumber: 4)
     }
+    if let v = self._uuid {
+      try visitor.visitSingularStringField(value: v, fieldNumber: 5)
+    }
     try unknownFields.traverse(visitor: &visitor)
   }
 
@@ -1841,6 +1861,7 @@ extension SessionProtos_CallMessage: SwiftProtobuf.Message, SwiftProtobuf._Messa
     if lhs.sdps != rhs.sdps {return false}
     if lhs.sdpMlineIndexes != rhs.sdpMlineIndexes {return false}
     if lhs.sdpMids != rhs.sdpMids {return false}
+    if lhs._uuid != rhs._uuid {return false}
     if lhs.unknownFields != rhs.unknownFields {return false}
     return true
   }
@@ -1853,6 +1874,7 @@ extension SessionProtos_CallMessage.TypeEnum: SwiftProtobuf._ProtoNameProviding
     3: .same(proto: "PROVISIONAL_ANSWER"),
     4: .same(proto: "ICE_CANDIDATES"),
     5: .same(proto: "END_CALL"),
+    6: .same(proto: "PRE_OFFER"),
   ]
 }
 
diff --git a/SessionMessagingKit/Protos/SessionProtos.proto b/SessionMessagingKit/Protos/SessionProtos.proto
index 4193d202c..052ae7e5f 100644
--- a/SessionMessagingKit/Protos/SessionProtos.proto
+++ b/SessionMessagingKit/Protos/SessionProtos.proto
@@ -54,6 +54,7 @@ message Content {
 message CallMessage {
 
     enum Type {
+      PRE_OFFER          = 6;
       OFFER              = 1;
       ANSWER             = 2;
       PROVISIONAL_ANSWER = 3;
@@ -68,6 +69,8 @@ message CallMessage {
     repeated string sdps            = 2;
     repeated uint32 sdpMLineIndexes = 3;
     repeated string sdpMids         = 4;
+    // @required
+    required string uuid            = 5;
 }
 
 message KeyPair {
diff --git a/SessionMessagingKit/Sending & Receiving/MessageReceiver+Handling.swift b/SessionMessagingKit/Sending & Receiving/MessageReceiver+Handling.swift
index 94196ac00..bf5263d50 100644
--- a/SessionMessagingKit/Sending & Receiving/MessageReceiver+Handling.swift	
+++ b/SessionMessagingKit/Sending & Receiving/MessageReceiver+Handling.swift	
@@ -269,17 +269,17 @@ extension MessageReceiver {
             if let current = WebRTCSession.current {
                 result = current
             } else {
-                WebRTCSession.current = WebRTCSession(for: message.sender!)
+                WebRTCSession.current = WebRTCSession(for: message.sender!, with: message.uuid!)
                 result = WebRTCSession.current!
             }
             return result
         }
         switch message.kind! {
+        case .preOffer:
+            print("[Calls] Received pre-offer message.")
+            // TODO: Notify incoming call
         case .offer:
             print("[Calls] Received offer message.")
-            // Delegate to the main app, which is expected to show a dialog confirming
-            // that the user wants to pick up the call. When they do, the SDP contained
-            // in the offer message will be passed to WebRTCSession.handleRemoteSDP(_:from:).
             let storage = SNMessagingKitConfiguration.shared.storage
             let transaction = transaction as! YapDatabaseReadWriteTransaction
             if let threadID = storage.getOrCreateThread(for: message.sender!, groupPublicKey: message.groupPublicKey, openGroupID: nil, using: transaction),
@@ -287,6 +287,9 @@ extension MessageReceiver {
                 let tsMessage = TSIncomingMessage.from(message, associatedWith: thread)
                 tsMessage.save(with: transaction)
             }
+            // Delegate to the main app, which is expected to show a dialog confirming
+            // that the user wants to pick up the call. When they do, the SDP contained
+            // in the offer message will be passed to WebRTCSession.handleRemoteSDP(_:from:).
             handleOfferCallMessage?(message)
         case .answer:
             print("[Calls] Received answer message.")