Making incoming call to Twilio number, I hear message from SAY verb but not tones of digits from PLAY

Question

Using the below code in a TWIML Bin, when I call my Twilio number I hear both SAY messages properly but just silence when I'd expect to hear the tone for [wait 1 second] 3 [wait 1 second] 3 [wait 1 second] 3 [wait 1 second] 3.

Any idea what I'm doing wrong? Thanks!

<?xml version="1.0" encoding="UTF-8"?>
<Response>
    <Say>Welcome</Say>
    <Play digits="ww3ww3ww3ww3"></Play>
    <Say>Goodbye</Say>
</Response>

Answer 1

The terminating carrier needs to play out the DTMF. Most DTMF is sent as events (RFC 4733) over SIP, so it is up to the terminating carrier to extract the events and insert them into the media stream. I hear them on Google Voice and Mint Mobile when calling this TwiML.