I got 2 of them for $20 each at Target during the Black Friday special, and had this problem happen to me. The 1st one hadn't been doing it, but before I could get a case for it it slipped out of my shirt pocket straight onto the concrete.
The 2nd one developed this problem. It would reboot & reboot & reboot sometimes for 15-20 minutes over & over, you couldn't stop it. (It seemed to do it worse once the battery reached 30% or so.) I have about 2 seconds of patience for something like that, and it ended up in splinters--this time, unlike the 1st time, ON PURPOSE.
It's ashame because to get it for $20 coming from a Kyocera Rise, it'd been fine for me had it not developed this problem. The call quality and screen clarity were fine, GPS locked on quickly, battery life was okay if not outstanding, and there was no "lag" or locking up as my Kyocera Rise would do and do often. I'd been content with it vs, say, a Galaxy S3, but reboots are totally unacceptable for me, they're a deal breaker--or, in this case, a phone breaker. You just don't do it. Period. DON'T DO IT.
The LG Optimus F3 went on sale at Radio Shack for $70 the Monday after that disastrous weekend, I grabbed it and have had none of those reboot problems, and it has 4G & better battery life to boot. Heck, I have gone 3 days at times without a shutdown or reboot, and it just goes right along rock-solid. THAT is how a phone should be, and OUT OF BOX too.
Short answer--get the LG Optimus F3, forget this piece of junk. You shouldn't have to do the phone equivalent of a lobotomy or engine overhaul just to stop extremely annoying reboots. It should do fine that way OUT OF BOX, AS IS.