the alltel rom does enable gps but if you do flash it then make sure you DO NOT let the customizations run.i am not 100% sure but here is a link to flash your radio only so you can keep your curent rom.
ftp://ftp.xda-developers.com/Vogue/Radio_Roms/ .the one at the bottom 3.42.30 is the newest alltel radio and is gps enabled. i hope this helps and be very careful if you do flash your radio as this can really mess your phone up if you do not finish the flash. You should go here first and use the imcokemans unlocker
http://forum.ppcgeeks.com/showthread.php?t=20370. as i said this is potentially dangerous so make sure to read more about flashing radios before you do this. and you have yo unlock your phone with the 2.31 unlocked first.