These variations on the same service let callers bill call usage to their own accounts, or their employers' corporate accounts, or a credit card.
Users can either dial the card number and PIN as prefix digits (before the address digits), or "swipe" the card through a reading device attached to the terminal equipment. The service then debits the cost of the call debited to the user's account (rather than to the renter of the telephone line).
This is particularly useful, for example, for making calls from pay phones without having to use coins. The credit-card calling service extends this capability to include direct billing to a bank credit card.