Voicemail not detecting for US T Mobile numbers.

conventional-black · 2025-05-14T15:54:46.891Z

"callId": "05160a81-d251-40d6-bdfa-d3c71d7b8434", voicemail detection is on. works for Indian providers but not for US.

V

This is a known issue: Vapi voicemail detection often fails for US T-Mobile numbers, resulting in "Silence Timed Out" even when detection works for other providers. As a possible workaround, try increasing your timeout settings in the configuration:

{
  "machineDetectionTimeout": 45,
  "machineDetectionSilenceTimeout": 8000
}

{
  "machineDetectionTimeout": 45,
  "machineDetectionSilenceTimeout": 8000
}

{
  "machineDetectionTimeout": 45,
  "machineDetectionSilenceTimeout": 8000
}

{
  "machineDetectionTimeout": 45,
  "machineDetectionSilenceTimeout": 8000
}

If the issue persists, there is currently no documented fix—monitor for updates or contact Twilio support for further assistance.
supportFails to Detect Voicemail Every Single Time

Sources:

⤵️ Mention @Vapi Support Bot for follow-ups 🐥

V

Vapi Support BotAPP•5/14/25, 3:56 PM

There are known issues with Vapi voicemail detection not working reliably for US T-Mobile numbers, often resulting in a "Silence Timed Out" status. One actionable step is to increase the

machineDetectionSilenceTimeout

machineDetectionSilenceTimeout

machineDetectionSilenceTimeout

machineDetectionSilenceTimeout value to accommodate longer silences in voicemail greetings. Try updating your configuration as follows:

"voicemailDetection": {
  "enabled": true,
  "provider": "twilio",
  "machineDetectionSilenceTimeout": 8000  // Increase to 8000 ms (8 seconds)
}

"voicemailDetection": {
  "enabled": true,
  "provider": "twilio",
  "machineDetectionSilenceTimeout": 8000  // Increase to 8000 ms (8 seconds)
}

"voicemailDetection": {
  "enabled": true,
  "provider": "twilio",
  "machineDetectionSilenceTimeout": 8000  // Increase to 8000 ms (8 seconds)
}

"voicemailDetection": {
  "enabled": true,
  "provider": "twilio",
  "machineDetectionSilenceTimeout": 8000  // Increase to 8000 ms (8 seconds)
}

If the issue persists, it may be due to provider-specific limitations for US T-Mobile numbers, as no confirmed fix is documented in the found information.

Sources:

S

spotty-amber•5/14/25, 4:43 PM

@Duckie @supportr we have set "provider": "vapi" as per recomendation. are you saying to use twilio?

V

Vapi Support BotAPP•5/14/25, 4:45 PM

Yes, the official documentation recommends using Twilio as the provider for voicemail detection. Update your configuration as follows for best results:

"voicemailDetection": {
  "enabled": true,
  "provider": "twilio"
}

"voicemailDetection": {
  "enabled": true,
  "provider": "twilio"
}

"voicemailDetection": {
  "enabled": true,
  "provider": "twilio"
}

"voicemailDetection": {
  "enabled": true,
  "provider": "twilio"
}

You can also optionally combine this with Vapi's built-in tool for improved accuracy. Effectiveness may still vary by carrier, especially for US T-Mobile numbers.
See documentation

Sources:

V

Vapi Support BotAPP•5/14/25, 4:47 PM

Based on the documentation and community feedback, it is recommended to use

"provider": "twilio"

"provider": "twilio"

"provider": "twilio"

"provider": "twilio" for voicemail detection in Vapi, especially when troubleshooting issues with US T-Mobile numbers. Update your configuration as follows:

"voicemailDetection": {
  "enabled": true,
  "provider": "twilio",
  "machineDetectionSilenceTimeout": 8000
}

"voicemailDetection": {
  "enabled": true,
  "provider": "twilio",
  "machineDetectionSilenceTimeout": 8000
}

"voicemailDetection": {
  "enabled": true,
  "provider": "twilio",
  "machineDetectionSilenceTimeout": 8000
}

"voicemailDetection": {
  "enabled": true,
  "provider": "twilio",
  "machineDetectionSilenceTimeout": 8000
}

This approach is the most supported and documented for your use case.
See documentation

Sources:

S

spotty-amber•5/14/25, 4:48 PM

@Duckie we will have all USA carrier and cant built carier specific voice mail settings. Is this always we will use provider as twilio and never vapi?

V

Vapi Support BotAPP•5/14/25, 4:50 PM

For supporting all USA carriers, the official recommendation is to always use Twilio as your voicemail detection provider in Vapi, since carrier-specific settings are not supported and Twilio is the most documented and reliable option for US numbers.

Update your configuration as follows:

"voicemailDetection": {
  "enabled": true,
  "provider": "twilio"
}

"voicemailDetection": {
  "enabled": true,
  "provider": "twilio"
}

"voicemailDetection": {
  "enabled": true,
  "provider": "twilio"
}

"voicemailDetection": {
  "enabled": true,
  "provider": "twilio"
}

You may optionally combine this with Vapi's built-in tool, but Twilio should be your primary provider for US carriers.
See documentation

Sources:

V

Vapi Support BotAPP•5/14/25, 4:50 PM

You should always use

"provider": "twilio"

"provider": "twilio"

"provider": "twilio"

"provider": "twilio" for voicemail detection in Vapi when supporting all US carriers, as carrier-specific settings are not supported and "twilio" is the only documented and recommended provider for this use case.

Here’s the recommended configuration:

"voicemailDetection": {
  "enabled": true,
  "provider": "twilio"
}

"voicemailDetection": {
  "enabled": true,
  "provider": "twilio"
}

"voicemailDetection": {
  "enabled": true,
  "provider": "twilio"
}

"voicemailDetection": {
  "enabled": true,
  "provider": "twilio"
}

There is no documentation supporting the use of

"provider": "vapi"

"provider": "vapi"

"provider": "vapi"

"provider": "vapi" for US carriers.
See documentation

Sources:

K

KyleAPP•5/15/25, 4:42 AM

Hey,

Could you please schedule a brief call at your convenience so we can discuss this matter in detail?

Kindly use the following link to book a suitable time: https://calendly.com/shubham-vapi/chat-30m.

C

clean-aquamarine•6/13/25, 3:03 PM

@Shubham Bajaj - I am curious if this is the same issue I am having.

K

KyleAPP•6/14/25, 1:34 AM

This ticket has been marked as solved, and as a result, you will no longer receive any further responses. Kindly create a new support ticket to escalate your inquiry. 

Voicemail not detecting for US T Mobile numbers.

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