US Mobile Wireless SIM card that uses T-Mobile network for the service. It will work your phone on US Mobile Wireless using their bring you own device option if your phone is a T-Mobile phone or an unlocked phone that is compatible with T-Mobile. For activation, you will need to go to usmobile.com (and buy a prepaid no-contract month-to-month unlimited plan)  This SIM cannot be used directly with T-Mobile for an existing T-Mobile account or  a new T-Mobile account. It can only be used with US Mobile Wireless service and plans. The sale is final. No returns.