Most of the time it is Advance Config or Diamond Tweak that were prone to the TP having these issues whcih make a change in the reg, it looks like it is also causing the same on the TP2.
If you have one of these two, check the data connection area, I for one dont use these program I do all my tweaks manual. I had this same problem on my TP back in the days and it was AC causing the issue.
If you are not afraid to mess with the reg, then check the setting in the reg to see if they have been changed.
This if from the TP Essentials:
http://forum.ppcgeeks.com/showthread.php?t=42730
"Issues with answering your phone when a data connection is open (answer buttons don't do anything)? Looks like a tweak messes up a registry key that affects this. [HKEY_LOCAL_MACHINE\Comm\ConnMgr\Planner\Settings], make sure SuspendResume is set to #777 (not anything containing GPRS). This issue seems to be related to Advanced Config."