I had alltel and switched to cingular but like my old phone better.

the answer is no. alltel operates on a cdma network, similar to cricket, verizon, sprint, etc who do do not require a sim card. Cingular, (almost pains me to say cingular now, im so used to the new name) aka AT&T operate, as you know, on a sim card setup, which means all AT&T phones contain a sim card slot which alltel does not feature. so, sadly, no, as frustrating as it sounds, no you cannot operate or unlock an alltel phone to cingular's network. it is physically and technically impossible.