Design and Implementation of a Callback service (Asterisk)

Looking for an implementation and design of a VOIP service. The system should do the following: When a user calls a service, the server should disconnect/hang-up and call back the user. Once called, the user should be able to call out via one of the specified sip trunks. Requirements: Deploy an Asterisk server Create a call back service Create and design a database of users for the service (MySQL) Registration form for the call back users Differentiate between users Authenticate users by caller id/password Different price plans *These options could be implemented after the original design have been completed Automatic user creation using PayPal I have quite a bit of experience with Asterisk, PHP and Linux, therefore inadequate applicants should not apply. Project schedule is between 3-14 days. Budget: 100$-300$