Yes, I'd be very surprised if it wasn't for both carriers.
Me too. What I think people tend to forget is that AT&T is rolling out their LTE service, but slowly. It's active here in Atlanta, but I don't believe that there is any "official" device taking advantage of it right now. Maybe data cards, but I don't think there is a phone for it yet.
My point is that a "multi-carrier" phone should be a given at this point- even if it has LTE. Speculation that the phone will be available on sprint and T-mobile give a little more validity to a multi-carrier phone as well.