I use my Galaxy S4 as one of the lines on my son's T-Mobile One plan. I just bought a new locked T-Mobile Galaxy S6. I want to move my T-Mobile account and data from my old S4 to the new S6. I want to buy a SIM card on Ebay. How do I be sure to get the correct one?

I know I should NOT get a prepaid one.

Should it be activated or unactivated?

My phone is locked.

Should I get one that is called a replacement or not?

Which SIM card should I buy?

See More: Which SIM card to transfer from S4 to S6 T-Mobile