Need pointers to a SN (service node) to deploy a call back service.

Hi,
This call back service has to be deployed on a GSM network.
Here based on certain criteria, the service node should call a party
(say A). When A answers the service node should
re-direct/connect/transfer the call to party B (who is chosen based on
some other criteria When B answers, A and B should be in speech
path.

On the billing front, A should be billed. This should appear as a part
of his regular bill.

If there is no such service node, then I inputs on how to develop one.
The design for this node should use industry standard (and existing)
features /services /messages /protocols to do the
"re-direct/connect/transfer". The billing requirement is an important
aspect to be considered in the design.

Thanks,
Rohith K N

PS for users familiar with IN: I am trying to build a service that
gives the functionality of the SCF initiated message "Create call".