VoIP Setup with reverse Calling and PAYPAL integration

We are looking for someone who can help us with developing an attractive and user friendly international calling website with secure payment processing (through PAYPAL) and those who has good knowledge in Asterisk/a2billing/Elastix. We need automatic user account creation after successful payment of PAYPAL. System should ask few basic Q's to register on site (including his Mobile number), a verification code (SMS) will be sent to user's mobile to verify his identity. This functionality will work throughout all the countries. Once user get confirmed his payment his account will be credited by the amount/package he chooses. For reverse call functionality, he need to dial a number using his registered phone, and after 2 rings his call will be declined by our system, system will recognize his identity and reversely call on his registered number once the call is answered by User he will hear his account credit balance in USD and IVR will ask him to call desired number followed by # key. once he press the # key system will again announce the time available for this call based on his credit balance. And call gets connected successfully. Additionally Following features required: ~ Apart from his main number, User can add as many as number he wish to add in his same account. ~ For corporate customers, 1 account Balance can be split & allotted to different employees of that organisation. ~ 2 or 3 types of rates list (for different retails or corporate customers) Only those have rich experience of development of these type of projects in past, should bid on this project.