If you are someone that is looking online for a good deal on a new phone, you may run across that perfect condition phone that just so happens to have a Bad ESN. So what does that mean? It’s basically the electronic serial number. For GSM phones, international capabilities, you also have IMEI identifications.
If a carrier finds a customer who either stops paying for their phone service or reports their phone as stolen, they will block these serials.
Learn more here.