Which billing solution would I recommend is a question i am asked almost daily.
The answer usually is - it depends on the requirements, budget, etc. We don't provide "one size fits all" billing - there is no such thing IMHO. Instead Thirdlane is open for integration and is known to be deployed with various billing solutions - open source or commercial.
That said, I just spoke with Erik Smith (eeman) about his experience using Voip Innovation's hosted billing. What I did not know is that it is possible to use their billing without being a trunking customer.
This could be a good option in some cases, and I am sure Erik could help with the setup if needed - right Erik?