T-Mobile does not currently offer SIM cards for free to existing customers as of April 2015. Lost, stolen, damaged or out-of-date SIM cards must be replaced by purchasing a new SIM card from T-Mobile's official website or over the phone.
T-Mobile offers SIM cards in the standard, micro and nano size formats at a price of $15 each. SIM cards may be discounted or free with the purchase of a new T-Mobile service plan or device. For users who are unsure of the SIM card size needed for a device, T-Mobile has a guide that shows each SIM card shape and size on its official website.