Nextel is owned by Sprint. This phone is a nextel phone, I cant see the model number, but i believe it says i826. The i stands for iden, which is the network its on, like GSM or CDMA. As far as I know, Nextel is the only carrier that uses the iden network, because of the 2 way capability of their phones. Iden is a slower network, and not good for phones with data plans, or that go online and surf the web. The iden network is good for 2 waying, which makes these great work phones, or good family phones so you can beep your kids, parents, brother/sister, quickly and get a quick response. For Tmobile your looking for a GSM phone, which takes sim cards. yes this phone takes a sim, but its different, its just for nextel phones. Ive needed a backup so ill be watching and bidding! Thanks!