One of the reasons that I stopped using Trixbox was because there was an ongoing problem with it as to how it handled DTMF codes. If you were calling a remote service such as a conference bridge or an automated payment system that required you to enter DTMF codes it would not pass them through properly so that the remote system could handle them correctly.
FreeSWITCH does pass them properly. However, this doesn't mean that you will avoid all problems. Beyond this point there will mostly be problems with client configuration.
I have Linksys and Grandstream ATAs. Linksys have an AUTO mode that selects the most appropriate method for DTMF handling (who knows how...) - it seems to work well. Grandstream require you to select for DTMF to be sent in Audio or in RFC2833 or in SIP info packets. If you select more than one of these options simultaneously you may cause yourself problems.
In early versions of FreeSWITCH it seems that the audio stream was somewhat muted while RFC2833 packets were being sent, however in recent builds this is not the case. So in an earlier build my Grandstream worked happily with audio AND RFC2833 being sent simultaneously, but in a later build this resulted in the far end being unable to understand the DTMF signals - as it was getting extra digits due to hearing both the RFC2833 packets AND the audio DTMF.
So if you have problems with DTMF being understood by remote systems, check to see if you are using more than one method of sending it.
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