Authenticating outgoing calls

Hello,

I am developing a software that connects to the GSM network through SS7. I need to have my software make calls on behalf of subscribers, and have them charged for the calls. So, I need to do the following:
1- Determine if the subscriber is pre-paid or post-paid
2- If post-paid, authenticate the called number (make sure the subscriber has access to call the required number, which might be international or premium).
3- Then make the call and log a CDR record for the billing system.
4- If pre-paid, make sure the subscriber has enough balance and deduct the call charge.

Can someone please provide me with guidlines on how to do steps 1, 2, and 4.