It does not require a contract.
You can (supposedly) use usb 3G/4G modems. I've heard the only ones usable are on the Sprint network. Clearwire 4G might since it's WiMax too.
Right now, the kinks and support are still rolling out. Don't expect everything to work right away perfectly. In fact, to make sure you can deal with what currently works, make sure the dealer has the navigation all set up before you test drive. Call them and tell them you intend to test it out completely.