If the Alltell is GSM Network mean you can use with Sony Ericsson Phone after unlock it,It's CDMA Network means you cannot unlock it...To unlock the phone from the Network lock you can use the Unlock code,you can get the code and instructions from here
Superunlockcodes.com and unlock it from Network lock...SO alltell is CDMA Network so you cannot use it with sony ericcson phone after unlock,You can use GSM Network like T-Mobile,vodafone and Orange.