For a modem, at least all DOCSIS modems the serial number will be totally separate and is used for authentication to the modem. Not 100% sure about FiOS as I do

For a modem, at least all DOCSIS modems the serial number will be totally separate and is used for authentication to the modem. Not 100% sure about FiOS as I don't have it but I'd imagine they would do something similar to the rest of the industry.