[mikejbradley]

Theoretically a hot spot / cell phone which uses a removable SIM can only be locked by a carrier who registers the MEID address of the device to a paricular person / cell phone number. If someone buys (or steals) the device and replaces the removable SIM, they cannot activate it with the same carrier unless the carrier allows it, since the carrier has a database which says this MEID/MAC address belongs to someone else. That would not prevent someone from using the device on a compatible competing carrier - TMobile for AT&T, Sprint for Verizon. The four major carriers are not 100% compatible, so don't just assume you can use an AT&T cell phone on TMobile. But Straight Talk Wireless supports both AT&T and TMobile phones on a BYOD plan. I'm not sure whether the MEID database is shared by all carriers, it might be. But I'm pretty sure the rule is now, that if a phone # or MEID is not connected to a cell/data plan for over 30 days, the carriers "cross it out" and recycle the MEID and the phone #, since I've bought cell phones which "used to have someone else's number" and voice mail for the prior owner of the number. That also means that usually a device which is sold as used, if the account it was attached to wasn't deactivated, the MEID will become available to re-register 30 days after the plan was cancelled for non-payment, or immediately after the MEID is removed from the account and replaced the the new device's MEID. This is what carriers do when people upgrade their phones, they deactivate the old MEID and replace it with a new MEID on the same account....