unfortunately, no because T-Mobile uses GSM technology, that's why they require SIM cards for their phones. Verizon, Sprint, and Alltel operate on CDMA technology and they do not use SIM cards. AT&T does operate on GSM, however you still could not use the Sidekick on the network because their features would be incompatible with the phone. Therefore, you may not use your Sidekick on any other network, because GSM and CDMA are two completly different technologies and they will not work with each other. Hope this helped out some.