WiMAX is a type of network, just like GSM or CDMA, so it's not exclusive to Sprint. Here's a list of the current worldwide proposed or deployed WiMAX networks:
http://en.wikipedia.org/wiki/List_of...WiMAX_networks
Here's a few more pics of the HTC T8290:
http://gizmodo.com/5061517/leaked-ht...-sharp-corners