I've been using a Pre 3 for a while and haven't had a problem like the one you describe. Are you using a customer Kernel from Preware? If so, please reload the stock HP Kernel and test some more. Are you using Wi-Fi and/or Bluetooth while on the call? If so, try turning those off while not in use. If neither of these help the problem, definitely contact HP.
Ridius
Please do not send me direct messages unless I ask you to. Random Direct Messages asking for support will be ignored. Please post your question/help request in an existing forum thread or create a new one so that everyone can benefit.
If you like IRC, feel free to drop by #webOShelp on Freenode. I hang out in there quite a bit.