IPhone :: Keeps Rebooting After Restart?

Whenever I try to shut off and restart my IPhone it stays on the apple logo start up screen for about 5 minutes then goes to the screen to slide to unlock and freezes so I cannot unlock the phone. Then after about 3 minutes it goes to a black screen with the round waiting symbol on it, then back to the slide to unlock screen again, then black waiting screen, then it reboots itself again and starts the process over. The first time this happened it went through the cycle 3 times. The next time I waited 2 hours and for it to work and finally went into itunes to restore it. I try holding down home and on/off buttons and it reboots it again, but nothing happens. So today my phone just restarted on its own when I was in Safari and after about 20 minutes I took it to the Verizon store to see what they can do about it. First they said to contact Apple support, then a guy held down the home and on/off button and then it unfroze. I told him I already tried that 2 or 3 times today since this problem started, but he didn't care because he was too mad he missed out on a sale to "help" me. So the phone works now, but I know if I just try to restart it again the phone will just go through the rebooting problem all over again. I have not dropped the phone and I thought restoring the phone would fix it if it was a software glitch, so I'm thinking it may be a hardware issue so what should I do if Verizon does not want to help me? I've had it less than a year so I would like to get it fixed before the warrently runs out.

Info:
iPhone 4, iOS 5.1