There's no device restrictions, plenty of people use this with Nexus 4s and the like. The catch is you can't get it in a T-Mobile store.
If you bring your own device, you have to either buy a SIM from T-Mobile.com and then put it in the device, or you can buy a SIM card kit from Wal-Mart.
If you bring your own device, you have to either buy a SIM from T-Mobile.com and then put it in the device, or you can buy a SIM card kit from Wal-Mart.