I had the same problem, but it was so bad I could hardly use the phone. In my case, the phone seemed to work okay if I kept it plugged in to the charger, but would start resetting itself 10 to 15 minutes after unplugging it. I took the phone in and had to get pretty aggressive to get them to exchange it, but the problem completely went away with the new phone. I suspected that the battery might have been defective. I point this out because they will try to get you to keep your battery with the exchange. I insisted they replace everything.
Hope this helps...