Are you new to T-Mobile? Install or replace a SIM card. Learn how to install or replace your SIM card with these easy to follow steps. Scroll to top . Have a new device or SIM? Select the link below that applies to you. You can also find one in a T-Mobile store. Postpaid accounts: See our SIM card page to check prices or order online. Buy a SIM card. T-Mobile SIM cards come with adapters, in case your device uses a nano, micro, or standard card. Added a new line of service, or upgraded your device? Can be used on unlocked, compatible GSM phones. You’re in the right place. You can also stop by a store. Prepaid accounts: See the Prepaid SIM Card page to check prices or order online. No SIM card activation required. Buy a new SIM card from T-Mobile.