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Yes, Nokia Series40 VoIP implementation supports sending of the DTMF (Dual-Tone Multifrequency) digits. The DTMF digits can be sent via the Options > Send DTMF command when the SIP VoIP call is active.
Series 40 supports sending of the DTMF digits in out-band. In which the signaling the DTMF digits are sent as RTP payload data as specified in IETF RFC 2833.