[danellis]

I've thought about the feasibility of such a service for a long time, but I always figured you'd run out of numbers. If there are nine digits available (16 - 6 - 1), that's 1,000,000,000. If you have, say, 100,000 customers, that's 10,000 per customer, which would quickly get used up if they're using one per transaction.

[dangero]

Couldn't you reuse a disposable number given some time interval?

[danellis]

I don't know enough about how it all works, but perhaps -- because the number isn't valid on its own -- giving the number to a different customer, with a different name, effectively invalidates its previous use and means it can be safely reused.

[andyjohnson0]

Some information here: http://en.wikipedia.org/wiki/Controlled_payment_number