I bought a Tmobile 3-in-1 starter kit and was using it on a prepaid plan. If I want to change to a postpaid plan would I have to pay for a new sim card?
I did, but my SIM was also from 2013. If your SIM is fairly new, you might be fine with your current SIM. Customer Care should be able to give ypu the best answer.
According to this thread answered by a Tmobile rep the answer is you will need a new sim.
prepaid to postpaid
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