AsteriskBilling.com - General technical and billing information for VoIP operators using Asterisk PBX.
The heart of any Asterisk billing software is the call rating engine. A good call rating engine should be able to support multiple rate tables so your different postpaid and prepaid service levels can have unique call rates associated. It should also be able to process the number of CDRs that you expect to generate both now as well as in the future as your company scales.
A good question to ask when comparing call rating engines for Asterisk is what programming language is the rating engine written in, and also how many calls can the rating engine in a given time period (hourly, daily, monthly, etc.)
While the size and complexity of your rate tables will factor into the equation, it is safe to say that a rating engine written in C or Java will perform much better than one written in a language such as PHP or Perl. It is also safe to say that fewer/simpler rates can generally be processed faster than more/complex rates. Keep these factors in mind.