You bought your iPad, now you need a case. And since you decided to purchase a Wi-Fi iPad instead of waiting for the 3G model, you're trying to figure out how the heck to connect to the Internet on those occasions when you're away from Wi-Fi.
Sprint is coming to your rescue. Their new 4G case for iPad is really just a nice case with a special pocket for one of their Overdrive 4G (US$349, less with rebates and 2-year activation) routers, which gives you a really fast connection to the Internet in those locations where Sprint has rolled out their 4G WiMAX service (see the Sprint site for details).
How fast is really fast? 3 - 6 Mbps, which is considerably faster than the 600 Kbps - 1 Mbps you'll get with 3G service. You have to purchase the Overdrive separately at a Sprint or Best Buy store, and of course the iPad doesn't come with the case, but if you have a need for speed and a new, naked iPad, this is a pretty nice solution.
If you're not currently in a 4G service area, the Overdrive 4G router also works well with Sprint's 3G data service. You'll also gain a lot of new friends when you share your 4G connection with up to four other people.