<div>In my experience DTMF works reliably only when sent over RTP using rfc2833. If you are using SIP, put this line under [general] section in sip.conf: dtmfmode = rfc2833. If you don't want to put this in [general], you can also put dtmfmode = rfc2833 in the declaration of each individual extension which you want to send DTMF using rfc2833.
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