its based on the coverage area you are in...when i first got my pearl it was always stuck in 1x mode, however i own a sprint mogul and i KNOW that my home has evdo a, so after a week of dealing with sprint i figured out they added the wrong blackberry pack to my account which on had vision, u need to make sure you have a PowerVision pack on your line and evdo is listed as a feature cuz that may be it.
*edit sorry, i am so used to being on a sprintusers.com i thought u had sprint, i dont know what to say now