Unlock

Are you using an iPhone of Android?  If you are using an Android, you can request a temporary SIM unlock through the SIM Unlock setting.  For a peanent SIM unlock, your device and account must meet all of the SIM Unlock Policy requirements. 

SIM Unlock Policy | Unlock Your Mobile Wireless Device | T-Mobile https://www.t-mobile.com/responsibility/consumer-info/policies/sim-unlock-policy