Hi
Some costs are described on the
www.star2billing.com website, which is the commercial arm of A2Billing, installing exactly the same version as A2Billing that is freely available from this site. Your version of A2Billing can be upgraded to 1.4. We put together star2billing to help support the project from a commercial perspective, and to support customers who either have A2Billing installed, or wish to install A2Billing.
In respect of the calling card, all you can do is give people the same PIN number. A2Billing is an accounts based system, not customer based.
Agents do not set rates, you need to set the rates on the agent's behalf, and allow him to sell your product. What you are talking about is in the realm of Reseller, that can be achieved by giving the Agent their own copy of A2Billing, either real or virtual.
There is no call-shop module. But the agent can top up or create accounts.
Callback could work in much the same way as above.
Joe