Call Problems with my HTC HD2!

[arms2serve]

Hey everyone,
I have been using the HD2 for the past few months. For the last month I have been having trouble with the most basic function - calls. People tell me when they call they hear a message saying that the phone is turned off although my signal quality shown on the phone is at the max. Then another problem surfaced, whenever I receive a call and I slide the Answer/Ignore bar to "answer" it gets stuck and the call continues to ring and eventually gets missed then it gets unstuck. This is happening with every call now. Basically I have three problems:

1. The incoming calls detect the phone as turned off when my phone is showing full signal strength.

2. And when the calls do manage to detect the the phone as "on" and I enthusiastically slide to answer, the slider gets stuck to "answer" while I wait until the phone stops ringing and the slider unfreezes.

3. When I call back the phone connects but after a few seconds I can't hear the person on the other end and have to drop the call.

I have switched my SIM to my old phone and it works perfectly. I have tried to "factory reset" the HD2 but the problem is still there. HELP!