Unfortunately it's more complicated that just having a SIM card (which would identify a GSM phone). AT&T is GSM but they use different frequencies that T-Mobile does. How that would effect using an old phone on T-Mobile is something you would have to look into.

Cricket is definitely CDMA. Not sure about Alltel.

Ok, thanks. They did flash my neighbors Verizon-

Verizon, Spring, Cricket, and other) use a cellular technology called CDMA (vs. GSM of AT&T and T-Mobile). CDMA phones lack a SIM card need to be programmed by the carrier. It may be possible for a carrier to reprogram a CDMA phone from another carrier. It's likely going to depend on the carrier and that specific phone.

Of course, most carriers with give you a free phone or sell you an inexpensive phone with a 2 year contract.

mike- the 2 year program is exactly what I want to get away from! I am looking at T-Moble prepay- will just have to go look at what phones they have i guess1 thanks

> Cricket is definitely CDMA. Not sure about Alltel

Alltel is/was CDMA. They were bought out by Verizon Wireless a few years back.