Verizon phones are CDMA so they don't use a SIM to connect to the carrier, so they can't be locked. (Locking means that you can't use another carrier's SIM card.) Even though the phone has a SIM card, that's for data, not for connecting to the network.
So it depends on which network you want to use it on, but forget AT&T or TMobil (or any of their mvnos). The phone doesn't have GSM hardware, so it won't work on GSM carriers. It won't work on Sprint (because they won't accept it) and if Verizon accepts it (on one of their mvnos) it doesn't have to be "unlocked".