htc mogul help please

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i currently have a sprint mogul that is flashed for crickett service...i recently moved and there is no crickett service around... i have tried going to the alltel store and get them to flash it to alltel but they say they cant.. the customer service ppl tell me they can when i call the 1800 alltel 1 number can someone please tell me what to tell the people at the store to get them to flash it for me, or what they need to change so i can help them help me! or if there is software that i can get myself to flash it myself.