Hi Deon, If you are looking for a billing engine (which I find it more suitable than complete billing system for hosted environments, same approach as FreeSWITCH +/or Kazoo - it does not enforce any business rules), take a look on CGRateS. It is opensource, very fast (12k+ requests per second), real-time, scalable (fire up more instances as you need them), feature-rich (multi-tenancy, supports advanced concepts as multiple calls out of same account, multiple balances inside one account, derived charging - eg: reseller chaining, grouped rating - charge using various billing increments within same call), API driven (full set of APIs available in both JSON and GOB) and production ready (runs already at MVNOs, ISPs, wholesale suppliers sites live). Happy to help you more! DanB