If you mean with the prepaid service, no unfortunately that's not an option. If you are on a no contract post paid plan (Even More Plus) or bought a phone without extending your contract you can add it.
Yes, but it's a little bit different. You deal directly with the manufacturer if you need to do a warranty claim and you have to send them the phone and then they'll send it back once they're done with it. Definitely not nearly as convenient.
I'm pretty sure the phone came with a 1-year warranty, because most phones do. If you bought it from a store, see if they have like an extended service plan.