I picked one up on ebay, and when I went into a Verizon store to get a SIM card for it, I asked the history on the phone. It was picked up from a Verizon store 3 months before I had it.
According to the rep, I had a full warrany on it and because of my Insurance, it also had an extended warrany (2 years). I had to do a swap (sleep of death), No issues with it and I still asked about warranty, still got like 7-8 months left before my extended warranty kicks in.
My advice, bring you phone into your carrier and see if they can find a history on the phone. If it's a Verizon phone, bring it to a Verizon store (not a 3rd party verizon store), same with AT&T/TMOUS. That is the only way to know for sure. All phones should be under warrany right now, as the phone has been out less than a year.... If they ask where you go it, tell a little white lie, that your brother or so gave it to you (keep in the family kind of thing)