What's the difference between SIM-free and T-Mobile SIM?

Which is most preferred phone company for the iPhone 5c or S?

A sim-free phone is just that, the phone is locked to the company that you buy it from & requires no sim. A t-mobile sim phone means the phone has a sim card in it, & it works with t-mobile. If you take out the sim card, the phone won't work. However, if you get the unlock code for the phone, then you can get a sim card from another carrier, put it in the phone, & it should work.

iphones first started with att. A contract was made between apple for att to provide the iphones & service. Verizon then made a contract with apple & was able to start carrying the iphone. I believe there are other carriers that are now carrying the iphones.
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