VoIP Audio Service API - DTMF tones cannot be played to telephony uplink in S60 3rd Edition FP2 (Known Issue)
The VoIP Audio Service (VAS) API provides a high-level interface to audio services on the S60 platform, designed especially for use in 3rd party VoIP applications.
VAS includes a DTMF player utility (CDTMFTonePlayer) that allows the playback of DTMF tones and sending them to the uplink stream of an active voice call. However, when used on S60 3rd Edition, Feature Pack 2 devices, output from DTMF player cannot be heard on the remote end.
No solution currently available. A possible workaround is to use pre-recorded DTMF tones and feed them to the telephony uplink using the VAS uplink stream.