To be honest, I don't know. It's just a software change you make, without opening the phone or anything. I think there shouldn't be a problem with the warranty. And if you break your phone, perhaps you can restore it using iTunes and pretend you never jailbroke it.
RAZR2 V9M. It's the Verizon model, which sucks because they lock a lot of features that are available on the same phone with other services. Verizon has a monopoly in my area because they have reliable service. I haven't had any problems with my phone, other than the fact that I can't have any fun with it without going through some very complex hacks or paying Verizon outrageous prices for simple crap like ringtones.