Well, since the phone is quadband it'll work in the US, but as the seller mentioned it is locked to the Vodafone network. This is fine so long as you unlock it (he says he will provide you with the unlock code), after which it'll be functional on any network.
The phone may have Vodafone branding, on the actual phone (Vodafone logo) and when accessing certain features (i.e.: mobile browser). Certain settings may also be set for Vodafone as well, although Motorola phones are supposed to be pretty easy to edit and customize to your liking (I've never done this but there's a lot of info and instructions on how to do it out there).
Apparently Cingular is going to be releasing it at some point, but I don't know if the release date has been determined. If Cingular is getting it though, and you don't mind waiting, you should just wait till they release it. It'll save you some cash and it won't be Vodafone branded.