I can't send DTMF when I try to log in to a conference bridge, what can I do?
First, make sure that you have the latest version of the software or at least 2.0.1.

Change DTMF method to "Inband" under MENU > SETTINGS > ADVANCED > *PIN CODE (1234)* > MEDIA > DTMF SIGNALLING > INBAND

Now the DTMF tones should work fine.