Anonymous Payment by Phone

Here is an idea for an anonymous payment system that would be useful for some applications.

• The seller sets up a phone number that charges N dollars per minute to any caller.
• The customer chooses a code, calls that number (which requires paying N dollars), and enters the code. A voice-generation system speaks the code back so the customer can confirm it.
• That code represents a payment of N dollars. The customer enters it in a web site, or a kiosk, and it constitutes payment for whatever.

It should be possible to do this using a phone card on a payphone or anyone else's telephone.