Phone Shutoff

Apple iPhone - Sudden Phone Shutoff

I have an original 3GS that has worked pretty much flawlessly since June of 2009. Suddenly this week it has decided to start dropping calls anywhere from, say, 2-3 to 15-20 seconds after the call is answered. First I thought it might be a proximity sensor error, dropping the call when I put the phone to my ear, but today it does the same thing in Speaker mode, about 10-15 sec after the timer starts. A Restart did not fix it, but after a full ("Hard") Reset it seems to be working so far.

I use this 3GS as my primary (and thus almost only) phone, using my home landline very infrequently, mostly for faxing. Thus I need to have it essentially "almost guaranteed" functional. Assuming it keeps working well today, is there any reason to take it to AT&T (local and easy), or the Apple Store (95 miles, not easy)?

iPhone ATT
I have the 3gs and had same problem w all my phones on my plan. Called AT&T and complained. Whatever they seemed to do solved my problem.

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That happened to me. Hardware problem. I had to take to apple and they replaced