LinuxDevices reports that Sprint is planning to release a WiMax enabled Nokia N800 Internet Tablet in the U.S. in 2008.

Sprint plans to provide WiMAX-based 4G wireless services available to over 100 million people during 2008. The first markets are supposed to be Chicago and Washington DC.
The WiMAX enabled Nokia N800 would still also support WiFi and Bluetooth.
More details on LinuxDevices.

In July Nokia announced Skype for the Nokia N800 Internet Tablet. It is somewhat surprising that WiMAX is an option for the N800, but 3G/UMTS is not. 3G networks are available now.