Hardware or Software problem?

Let me start by saying that I bought my 3GS a few months ago. It's never been dropped, jarred, bumped, wet or even slightly abused in any way. I hardly use it. My talk time is on average 80 min/month and I only send about 30 text msg. I'm trying to convey that my phone is very lightly used and taken care of. I've been noticing lately that my phone will have No Service in areas that should have full bars and 3G like in the middle of town. I can turn off my phone and turn it back on and then it'll show full service 3G in the same spot that was no service before. A few days ago it happens again. I'm in the downtown area of a large city and go to make a call but have no service. I power the phone off then power it up and it works (full bars/ 3G) but about 2 minutes later I get a "Restore Needed" on the phone. I go home so the Restore but Itunes says something about not having a SIM card installed or entering the password for one. I find a workaround for this on apple support by holding the home button down while connecting the USB and it works temporarily. I get my Iphone restored but now after a couple of hours the Restore Needed comes up. Sometimes I can power it down and back up and it'll be activated and work and other times I'll have to do a full restore in Itunes. Anyone else have this problem? I've restored my phone about 6 times and it'll work fine for a while (sometimes a full day) then it'll say 'restore needed' again.