They ALL have built in gps, and it works great, not sure what "Rom" (software) you have on yopur phone now and if it supports gps or not but, you should read a little bit and go and use the Unlocker (for flashing new roms (software) onto your phone) and you will be good to go.
Use unlocker 2.31 to enable you to flash with any Roms
http://forum.ppcgeeks.com/showthread.php?t=20370
Flash with a new official rom to upgrade your "radio" to the newest version.
http://www.htc.com/us/SupportDownloa...cat=2&dl_id=66
Edit out
I posted his diamond one, I have a diamond to, but just look in the upgrade for another)
It's all Very easy just spend a little while a few hours should do it, and do a little reading and It will be a breeze....the roms and such are in the "upgrades" forum at the top of the page here.
You are in the right place, a lot of sprint reps know next to nothing about the phones they are selling.