AT&T Tilt 2 bluetooth phone saga

[monza66mo]

My new Tilt 2 paired and worked fine for 7 months. A few months ago I was no longer able to answer an incoming call or make an outgoing call even though it would pair just fine. I deleted, restarted and re-paired the two several times. The best it will do is:
I can make a call using the handset (phone) to dial and hear it over the speakers.
I can answer a call using the handset and mute the car speakers (ringing continues over the speakers even though the call is connected).

I called AT&T and the said it is the car.
I went to the dealer and they said it's the phone.
I wiped the phone completely to restore factory settings and it does the same thing.
I used the phone warrante to get a replacement phone and it does the same thing.
I've used 6 other phones that pair and work correctly with my car.
My phone will pair but not work in a 2011 Camaro that I tried at the dealership.

I'm convinced that the trouble is with the AT&T Tilt 2 (by HTC) but I can't get AT&T or HTC to fix me.

Anyone have any ideas???

[monza66mo]

No one else has this problem?