asterisk users - Sep 2007 - DTMF Problem with International Calls

Hello All,

Does anyone knows a good carrier who can pass DTMF tone while doing Call 
Back? Currently, the Call Back system works within US, but as soon as 
international users tries to enter phone number the system does not 
understand the tones.

I tried to change the sip config to inband, auto, RFC2833 but it didnt 
work... So I suspect its my VoIP Carrier who doesn't pass the 
International DTMF tones.

Any suggestions?

Cheers,
Nitesh