I am certainly not an expert by any stretch of the imagination, but here's my 2 cents worth anyway.
There are several people on here that "Cook" ROMs. Get someone to cook a completely clean ROM. Just WinMo and a dialer. Flash that and see if it works. One thing I did notice about your post, you didn't mention installing a Carrier CAB after flashing to the Alltel ROM. You will need to do that. I searched for a carrier CAB for CellCom and didn't find one, I did however find a thread discussing how to get around it.
http://forum.ppcgeeks.com/showthread.php?t=42005
Make sure your radio is new, I am with Alltel and my radio version is 3.42. I don't think that the radio is provider specific. I do know that there are newer ones out there.
After getting the clean ROM on the phone, if it works, you can start adding back apps one at a time to see where your problem lies. Hopefully, the issue isn't a hardware problem.
I don't know that it will, but I hope this helps.