Here's unsolicited recommendation for paid support with a2billing.
If you are serious about installing a2billing above v1.3.4 then I highly recommend hiring Star2Billing for a managed install. Unless you are extremely confortable with both linux and sql databases, a2billing installation is at best complicated to install for someone new to linux. In my opinion it is best to simply hire Joe to work with you to guide you, or to have them just pop it in for you. It's rough enough to configure it to your project specifications, let alone install it. Joe does a magnificient job with paid support and the few dollars spent is well worth the price. No, I derive no benefit from this recommendation. I'm just a satisfied customer of the paid support program.