If you’ve read this thread http://www.voipwonders.com/2008/04/24/configuring-3cx-phone-system-with-cbeyond-sipconnect.html/trackback you’ll see my comment about needing to disable RFC2833 and SIPInfo for DTMF.

This is very easy in 3CX client, you simply uncheck the option under DTMF under connections. for Xlite client, it is hidden away in the advance menu. First you need to access the advanced menu, you can do this by dialing ***7469. Now filter for 2833, the first option should be rtp:2833:enabled, change the value to 0 (default is 1). Also while in advanced menu, filter for DTMF and make sure system:dtmf:force_send_in_band is set to the default of 1.

This will set Xlite to use INBand DTMF and your touch tones should now work.