What do UNLOCKED cell phones mean?

Question

does it mean you can put a sim card in and use any provider like a tmobile phone with verizon sim card.

Answer 1

Unlocked phone means you can use any compatible SIM card from any GSM carrier worldwide on your phone. The process is called SIM unlocking. And it just basically removes the restriction set by the phone manufacturer and service provider, which prevents the owner of the phone from using just any SIM cards from different carriers.

To learn about unlocking phones, there is a unlock guide at http://globalunlock.com/phones/