So if the ESN is currently bad because of an unpaid bill, Verizon will release the bad ESN after 6 months and the phone can be reactivated with a new Verizon plan, correct?
It's locked to version. The iPhone 4s is a cdma/gsm. They're all made the same but for every company the operating systems and programming are a little different. It can be used on other networks though, if you pay to have it flashed.