What is a JV block on an iPhone

Apparently “JV lock” is a synonym for carrier lock - or perhaps a reference to a particular flavor of carrier lock. (Edit: Or maybe, as Mac Jim ID surmised, JV might refer to an attempt to cheat the system.)

If a phone is carrier-locked, that means you can’t use SIMs from any other carrier. Only the carrier who holds the lock can release it - if they choose to do so. You cannot release the lock, we can’t, and Apple can’t.

A carrier unlock can only be done by the carrier that locked it. The JV SIM is an attempt to bypass the lock or to use the carriers network and is short lived. Eventually they catch on and you are out of luck.