i had something similar happen today. i got a call, but then when i tried to hang up, it showed the green bar at the top. i tried to click on that, but it kept closing. then when i pressed on the phone button to make calls, it would crash back to home every time. i turned the phone off, then back on, but that didn't help, so i had to restore the entire firmware.
My Iphone 3G is also experiencing the same problem. When i click end call the button blinks but yet nothing happens the call doesnt end. I have to wait for my friends to hang up for the call to end. If im speaking with an 800 number then the only way to end the call is to reboot during the call. This issue is only intermittent. About 30 percent of the calls. But just enough for it to be extremely inconvenient and frustrating. Ive called apple and they walked me through an entire software install which worked for a couple days but now again the same issue? any suggestions?
I assume that when you talked to AppleCare, they had you restore the phone and that's what you meant by "entire software install"? If for some reason they didn't have you restore then do that. Is it possible for you to take it into an Apple Store or AT&T Store? They would be able to fix the problem or replace the phone if necessary if it is under warranty. Have you tried ejecting the SIM card and reinserting it? That may help.