I used to sell used cell phones on eBay. Verizon, AT&T, and T-mobile (and perhaps others) phones could be unlocked by calling the original provider’s customer service line to ask for the unlock codes and providing them the IMEI or ESN. Call from another phone because there’s sometimes a need to cycle the device off and on. Keep in mind that if the phone was never paid off with its initial contract, customer service may be unable to provide you the unlock codes.
If you meant breaking a PIN, search for instructions on how to do a hard reset and be prepared to lose everything on the device.