Asterisk , VOIP

We are a VOIP provider and we need solutions for our existing issues in the Asterisk server. "Only serious bidders can bid- Please do not spam with recycled application" "Experience in both Asterisk and A2Billing is a must" The job description is given below, however, the first two points will be done in this bid, and on successful completion , the other points will be done. 1) The asterisk server should be checked for the registration fail of the phones 2) The dial plan should be reviewed for the disconnection of the phones at times and unsuccessful call completion 3) New Dial plan should be written for the usage of multiple terminations for selected countries 4) A2Billing should be customized according to our need. 5) Chances are there to write web services which may talk to the application . Optional expectation: 1) ability to program in .NET 2) Knowledge of A-Z Terminations 3) Knowledge of Calling Card solutions