All LTE phones (Android, iPhone, anuything) on VZW are GSM unlocked for the bands the phone supports. This is a restriction placed on Verizon due to the terms they sigend with the FCC for use of the 700 MHz spectrum for LTE.
An iPhone 5 will work fine on T-Mobile or AT&T's GSM networks with 3G. They are not compatible for LTE due to the hardware included in the phone.
If you want to tell, borrow a nano-SIM from someone with an AT&T or T-Mobile iPhone 5, place it in your phone, and watch as it works.