Small Billing system for Asterisk.

Dear Freelancers, We are in need for a small billing system (pre-paid) to control automated voice campaigns using asterisk .call files. The main idea is work with ".call files" using audio recorded files uploaded by customers and dialing-out for a large number of phones. (P.s.: based on initial-end date/time) The system needs to collect data from cdr's on mysql and apply charges to customer's based on rating plans and call duration time. (since this is a pre-paid system, we need to have an AGI to check balance before allowing the call to proceed.) System should have admin/customer interface with nice user interface ; also integration with paypal. PHP , Ajax and Advanced Asterisk skills are essencial for this project.