The Windows Phone 7.5-upgradeable Quantum C700 supports AT&T UMTS 850/1900 MHz frequencies, as well as quad-band GSM. As an unlocked phone, it can be used with Simple Mobile and TracFone’s new unlocked SIMs that grant access to both AT&T 3G/4G, as well as T-Mobile GSM networks for superior coverage.
The phone is one of the few Windows Phone 7.5 first-generation devices to feature a slide-out QWERTY keyboard. While it is unlikely to receive future firmware updates, it is considered as being compatible with all Windows Phone 7.5 “Mango” apps, and also is viewed by many in the hacking community to be a capable tethering phone with sideloading capability.
We only suggest this phone however for people that will primarily be using AT&T’s 3G or travel to countries with compatible 3G frequencies like Australia. The phone will only function at GSM/EDGE 2G speeds on T-Mobile, and is not compatible with any other US networks.