[robsta]

As everyone said, just watch your data usage, you don't want an insane bill because you went over your "unlimited" cap.

I have personally played online with a 3G connection and it works fine. I've played World Of Warcraft, Xbox Live (Halo 2/3, Call of Duty: World at War, GRID), and Call of Duty 4: Modern Warfare PC online just fine with no lag, however the latency is higher than everyone else who is on a wired connection and your "bars" will suffer on online gaming because of it, but that never affected game play for me.

Don't use a cellular router, unless you want an "always on" connection, which you still could do without the router, but your computer would have to be kept on 24/7. Just hook your air card into your computer and then run an Ethernet cable from your computer into your Xbox, then bridge the connections. If you need more details let me know.

You can also get the HTC Wifi Tethering App (for your Touch Pro) and get an Xbox 360 Wifi Adapter, that works too.

On Sprint, I know the cap for phones is 5GB of data per month, don't really know about AirCards.