Hello,
I have experience to work on Asterisk around 4+ years with wwwDOTaamrasolutionsDOTcom. Here I have added few of my major worked which I did on VoIP: 1. Fixed bugs in voicemail app in the early version of asterisk. 2. Integrated HASP in asterisk code. 3. develop a prepaid app for asterisk where I added similar functionality that you want. 4. added RADIS to support RBS VoIP billing system. 5. Implemented CEPT E1 in "libpri" driver for small Air Craft sponsored by wwwDOThoneywellDOTcom. 6. Developed a SIP softphone. You know it is quite difficult to implement any new features if someone don't have previous experience. So I think I will be your best choice to accomplish this. In addition to, I have 7+ working experience and working with some very large company like EA Spots. Open to mention that I am a very beginner in this free lancing arena. Thanks, Mahabub