What is a phone unlock box?
I believe you are referring to the "black boxes" that are used to hack the software in mobile phones and "unlock" them. Most cell phones are sold with proprietary software that enables them to only be used by the carrier that sells them. Once a phone has been "unlocked" it can be used on any compatible network (still needs to operate on the correct frequencies). They are priced based on what people are willing to pay for them. There are businesses out there that do nothing but charge people to unlock their phones.