iPhone 3G keeps needing to be restored

My iPhone has worked fine the past year and a half, but recently hasnt been working. It was getting no service in areas where there is service a week or so ago. Two days ago it said iPhone cannot make or receive calls restore needed. I did the restore and it has done the exact same thing at least 5 times. Sometimes it is going to the recovery mode screen when I turn it on. Ive done a DFU as well and the same things are happening. Any ideas on what to do?