Does anyone know a free or lowcost billing solution which works with SER, before i've tried with some commercials ones but they do not worked with SER and they were Radius Supported ones so was creating its own database.

All i need is a few simple PHP files so i can add/remove users from there and a add table for rating depending on prefix and it should use SER's database which is already created. And do sample calculations for me, enter user id/loginname/callerid or whatever and show me caller/callee/duration/time/date/cost and under all a grand total with tax space. So simple but i do not know how to do in PHP. Even some examples or good URL's to read are fine for me.