I am getting mix reports of users with 7900 series phones that call an outside auto attendant (not unity, another business over PSTN) and are unable to navigate the DTMF menu. For example if they punch 2 for english they get an "invalid response". The odd thing is that this is not always recreate-able. It does seem to happen to the same users when it does happen.
The most recent report are 7921 and 7971 users that use an MGCP gateway (digital PRI) to connect to the PSTN. I have "MGCP DTMF-Relay voip mode all codec out-of band" specified on the gateway as well. Not sure what could be impacting DTMF.
There are two prominent issues for this:
Basically most of the 12.4(15)T gateways, and any mainline IOS before 12.4(23), starting at around 12.4(13) or so.
Phone loads 8.4.1 or 8.4.1SR1 will cause duplicate DTMF when it's pressed on the handset. Speakerphone and headset shouldn't be affected.