If you google usually you can find a guide for your phone on HTC or other developer/modder/hacker forums for smartphones. It involves getting codes specific to your phone and using some software and a USB data cable to upload new settings to the phone. It's similar to firmware flashing.

Oh yeah, and they really really don't like you to do it because you're basically using parts of the network they don't want you to use. So whatever you do, don't tell Sprint customer service.