Sounds like you was trying to jailbreak your phone... that voids the warranty. However if you wasn't trying to jailbreak it, then try rebooting your phone into recovery mode and select "wipe all user data". It is basically a factory reset. If all else fails, just call your carrier and ask them.
If you can receive picture messages then you should be able to send them to your phone from myxer.com, free ringtones website. Doesn't matter what phone you say you have when you setup you account on myxer, just as long as you say you have an AT&T carrier. You get access to more free ringtones...