If you pay for the service after consuming it, you are by definition using a line of credit.

For cable you'd have to load a prepaid balance into your account, from which the the cable provider could debit by usage. As soon as the balance hits 0, service is shut down.

Most people don't want to deal with that hassle.

I believe that is actually because of the billing period. You're billed at the end of the usage period rather than the beginning.

With verizon FiOS I am billed at the beginning of the month and yet I still had to hand over my SSN. Who else am I going to go to, Comcast? I paid for the first month's service when I signed up and I pay for each month before the beginning of the month. For example, I paid for 11/02 to 12/01 on or before the due date which was 10/27. In other words, I paid for the month of November before November began. I have no Verizon equipment. The ont was already here when I moved here. I bought my own modem/router. I can provide proof if you don't believe me.

its billed in arears i assume.