diff --git a/app.js b/app.js
index c862deb..a0832ef 100644
--- a/app.js
+++ b/app.js
@@ -17,12 +17,21 @@ ExpressWs(app);
 
 const PORT = process.env.PORT || 3000;
 
+async function getCallerNumber(call) {
+  const accountSid = process.env.TWILIO_ACCOUNT_SID;
+  const authToken = process.env.TWILIO_AUTH_TOKEN;
+  const client = require('twilio')(accountSid, authToken);
+
+  const response = await client.calls(call.callSid).fetch();
+  return response.from;
+}
+
 app.post('/incoming', (req, res) => {
   try {
     const response = new VoiceResponse();
     const connect = response.connect();
     connect.stream({ url: `wss://${process.env.SERVER}/connection` });
-  
+
     res.type('text/xml');
     res.end(response.toString());
   } catch (err) {
@@ -30,6 +39,49 @@ app.post('/incoming', (req, res) => {
   }
 });
 
+const activeCalls = {};
+
+function bindCall(call) {
+  const { streamSid, gptService, streamService, transcriptionService, ttsService, marks, ws } = call;
+
+  let interactionCount = 0;
+
+  transcriptionService.on('utterance', async (text) => {
+    // This is a bit of a hack to filter out empty utterances
+    if(marks.length > 0 && text?.length > 5) {
+      console.log('Twilio -> Interruption, Clearing stream'.red);
+      ws.send(
+        JSON.stringify({
+          streamSid,
+          event: 'clear',
+        })
+      );
+    }
+  });
+
+  transcriptionService.on('transcription', async (text) => {
+    if (!text) { return; }
+    console.log(`Interaction ${interactionCount} – STT -> GPT: ${text}`.yellow);
+    gptService.completion(text, interactionCount);
+    interactionCount += 1;
+  });
+
+  gptService.on('gptreply', async (gptReply, icount) => {
+    console.log(`Interaction ${icount}: GPT -> TTS: ${gptReply.partialResponse}`.green );
+    ttsService.generate(gptReply, icount);
+  });
+
+  ttsService.on('speech', (responseIndex, audio, label, icount) => {
+    console.log(`Interaction ${icount}: TTS -> TWILIO: ${label}`.blue);
+
+    streamService.buffer(responseIndex, audio);
+  });
+
+  streamService.on('audiosent', (markLabel) => {
+    marks.push(markLabel);
+  });
+}
+
 app.ws('/connection', (ws) => {
   try {
     ws.on('error', console.error);
@@ -37,74 +89,66 @@ app.ws('/connection', (ws) => {
     let streamSid;
     let callSid;
 
-    const gptService = new GptService();
-    const streamService = new StreamService(ws);
-    const transcriptionService = new TranscriptionService();
-    const ttsService = new TextToSpeechService({});
-  
-    let marks = [];
-    let interactionCount = 0;
-  
+    let call = null;
+
     // Incoming from MediaStream
     ws.on('message', function message(data) {
       const msg = JSON.parse(data);
       if (msg.event === 'start') {
         streamSid = msg.start.streamSid;
         callSid = msg.start.callSid;
-        
-        streamService.setStreamSid(streamSid);
-        gptService.setCallSid(callSid);
-
-        // Set RECORDING_ENABLED='true' in .env to record calls
-        recordingService(ttsService, callSid).then(() => {
-          console.log(`Twilio -> Starting Media Stream for ${streamSid}`.underline.red);
-          ttsService.generate({partialResponseIndex: null, partialResponse: 'Hello! I understand you\'re looking for a pair of AirPods, is that correct?'}, 0);
+
+        getCallerNumber(msg.start).then((number) => {
+          if (activeCalls[number]) {
+            return;
+          }
+          console.log(`Twilio -> received new call from ${number}`);
+
+          const transcriptionService = new TranscriptionService();
+
+          call = {
+            callSid: callSid,
+            streamSid: streamSid,
+            gptService: new GptService(),
+            streamService: new StreamService(ws),
+            transcriptionService: transcriptionService,
+            ttsService: new TextToSpeechService({}),
+            marks: [],
+            ws: ws
+          };
+          activeCalls[number] = call;
+          bindCall(call);
+
+          call.streamService.setStreamSid(streamSid);
+          call.gptService.setCallSid(callSid);
+
+          // Set RECORDING_ENABLED='true' in .env to record calls
+          recordingService(call.ttsService, callSid).then(() => {
+            console.log(`Twilio -> Starting Media Stream for ${streamSid}`.underline.red);
+            call.ttsService.generate({partialResponseIndex: null, partialResponse: 'Hello! I understand you\'re looking for a pair of AirPods, is that correct?'}, 0);
+          });
         });
       } else if (msg.event === 'media') {
-        transcriptionService.send(msg.media.payload);
+        if (call && call.transcriptionService != null) {
+          call.transcriptionService.send(msg.media.payload);
+        }
       } else if (msg.event === 'mark') {
         const label = msg.mark.name;
         console.log(`Twilio -> Audio completed mark (${msg.sequenceNumber}): ${label}`.red);
-        marks = marks.filter(m => m !== msg.mark.name);
+        if (call && call.marks) {
+          call.marks = call.marks.filter(m => m !== msg.mark.name);
+        }
       } else if (msg.event === 'stop') {
         console.log(`Twilio -> Media stream ${streamSid} ended.`.underline.red);
+
+        for (const k in Object.keys(activeCalls)) {
+          if (activeCalls[k] && activeCalls[k].callSid == callSid) {
+            delete activeCalls[k];
+            return;
+          }
+        }
       }
     });
-  
-    transcriptionService.on('utterance', async (text) => {
-      // This is a bit of a hack to filter out empty utterances
-      if(marks.length > 0 && text?.length > 5) {
-        console.log('Twilio -> Interruption, Clearing stream'.red);
-        ws.send(
-          JSON.stringify({
-            streamSid,
-            event: 'clear',
-          })
-        );
-      }
-    });
-  
-    transcriptionService.on('transcription', async (text) => {
-      if (!text) { return; }
-      console.log(`Interaction ${interactionCount} – STT -> GPT: ${text}`.yellow);
-      gptService.completion(text, interactionCount);
-      interactionCount += 1;
-    });
-    
-    gptService.on('gptreply', async (gptReply, icount) => {
-      console.log(`Interaction ${icount}: GPT -> TTS: ${gptReply.partialResponse}`.green );
-      ttsService.generate(gptReply, icount);
-    });
-  
-    ttsService.on('speech', (responseIndex, audio, label, icount) => {
-      console.log(`Interaction ${icount}: TTS -> TWILIO: ${label}`.blue);
-  
-      streamService.buffer(responseIndex, audio);
-    });
-  
-    streamService.on('audiosent', (markLabel) => {
-      marks.push(markLabel);
-    });
   } catch (err) {
     console.log(err);
   }