Misc. Dialplan Tools start dtmf

From FreeSWITCH Wiki

You can use start_dtmf in a dialplan to enable in-band DTMF detection (i.e. the detection of DTMF tones on a channel). You should do this when you want to be able to identify DTMF tones on a channel that doesn't otherwise support another signalling method (like RFC2833 or INFO).

For example:

   <extension name="ivr_demo">
     <condition field="destination_number" expression="5000">
       <action application="answer"/>
       <action application="start_dtmf" data="true"/>
       <action application="ivr" data="demo_ivr"/>
     </condition>
   </extension>

The start_dtmf line listed above starts the start_dtmf application on this channel to allow for DTMF detection.

WARNING: Do not use the start_dtmf application and the start_dtmf_generate application together. If both are running at the same time you will cause a feedback loop to occur within FreeSwitch itself, such that a DTMF tone from a caller will result in repetitive DTMF tones being identified by FreeSwitch.