My IPhone 3GS constantly reboots itself. Is there a fix for this? Ive already had it to the ATT store where they told me that my contract is up for renewal so I can get a new phone as well as a new contract. Thats not going to happen.

My Iphone 3GS constantly reboots itself every 3 minutes. I took it to ATT they said to take it to the apple store because its "Just out of warranty" also my contract is up, so they wanted me to sign a new contract to get a new phone.

Ive done the hard reboot several times and it kinda worked for about a week, then yesterday I was back into ATT about a billing issue and told them to shut off my service and all of a sudden the phone starts to reboot non stop. There is not using it anymore at this point. Apple stores are way out of the way for me to just stop in one of them.