Swatch T8 Unlocked Smart Watch for Android Smartphone - Black Support for GSM 850/900/1800/1900, AT&T, T-Mobile Unlocked Sim card, Sprint Sim card is NOT ok with Bluetooth Dialer, Call Reminder, Bluetooth Call,Bluetooth SMS/IM Message Notifier with Anti-lost, Remote Capture,Health Management: Pedometer, Sleep Monitor, Sedentary Reminder,Calendar, Audio and Video Player could be used as a standalone cellphone when you insert a sim card into the watch could be used as company of your smart cellphone without insert sim card. The watch band length is fit for boys/girls and teenboys and teengirls or adult whose wrist diameter is not over 6cm