There's a local guy on Craigslist I was considering buying a used (month-old) iPhone from. Let's say it dies three months from now- will I have any warranty issues? I will be hacking it to run on T-Mobile, not AT&T. Also, as a side question- can iPhone firmware be downgraded? I realize we know little about 1.1.3, but my question is asked because if I order an iPhone from Apple and it has 1.1.3, I'd like to be able to downgrade to 1.1.2 for jailbreaking and unlocking.