Callback system Asterisk+A2billing

We are looking for a developer, or a group of developers, to build a simple callback system based on Asterisk and A2Billing. The system's specifications are: 1) System must be highly and easily scalable (by building clusters of Asterisks+A2Billings); 2) System must be all OSS based; 3) System will be all prepaid, based on "virtual" card numbers sold online or at stores; 4) System must provide access to callback initiation through WEB/WAP, SMS and IVR, with respective interfaces; 5) System must provide a simple Web interface for users/agents to buy cards and for users/agents to recharge cards; 6) System must provide a simple Customer Service module, enabling CSRs to add credits to specific card numbers and to list calls made per each card account; 7) System must provide a general reporting interface enabling admins to generate reports of total value of cards sold and recharged per agent; 8) System must provide a simple interface for admins to create card batches; 9) System must have multi-layered LCR for VoIP providers to complete callback calls. As all those features are already built in the Asterisk+A2Billing combo, we just need the developer, or developers to integrate all the necessary modules and to customize and simplify the interfaces on order for them to fit into our system concept. The developers must also build a simple website template including the web interface for users/agents, as per point 4, and a secure payment system. Further explanations will be given to the winner bidder.