Unable to hang up phone call I'm using a relatively new G2, and when dialing today, the call did not complete. It stayed in dialing forever. The hangup button did not work. I tried to force a connection failure with airplane mode, that did not work either.

Any ideas on what do in this situation? Ideally, I would like to know how to gather more data on the problem, so I can report it to T-Mobile and/or Google.
I'm guessing the Dialer froze.  Try holding the Home button, going into Task Manager, and killing the dialier process.

As Matt mentions in the comments,


  You can do the same thing from the home screen by pressing menu then going to settings > Applications > Manage Application then choose the "phone" or "dialer" app and click "stop"