I'm Italian but my company is based in thailand, i am very expert in A2Billing (voip in general), I made a lots of a2billing customizations, someones deep core, recently i made for one customer a bridge for a social network based on joomla and easysocial / joomsocial (web site made too), also made a series of ad hoc API for exchange with mobile sip softphone app always customized by us, if you interest i can organize one server demo for you with A2Billing and all customization (A2Billing cusomization) that i make to show you what can do and that really can customize all in A2Billing. Feel free to contact to me and ask everything about you need. Best Regards