Hi
We can do it with 10 numbers by using the speed dial facility - we have an addon module,
http://www.asterisk2billing.org/add-ons ... peed-dial/This is dialplan that identifies the customer, looks up the associated speed dial number entered via the interface or via an IVR, then calls that number.
To do more than 10 would require that you modify A2Billing to allow more speed dials, but for the vast majority of people, 10 is more than sufficient, which you can confirm yourself if you do some analysis on your existing traffic and look at the number of unique dialled digits by customer.
Joe