There are 2 versions of this phone.
One version is GSM. I am not sure if this is a 2G GSM or 3G GSM. If it is a 2G GSM, you may need to ask T-Mobile or any company that uses T-Mobile Towers. As of this year, AT&T (Includes Cingular and Cricket) has shut down all of its 2G support on its footprint.
The second version is CDMA. You will need to ask Sprint, Verizon, or any one that uses their towers to see if this phone can be used on it.