I’m afraid that the answer is far longer than the question. There are a lot of VoIP billing providers in the market place and your selection should start by looking at your short and long term goals.
There are a number of packages on the market that are designed for the small to medium sized operation, for example 4 analogue ports up to 4E1’s. These are typically priced accordingly and you should be able to get yourself a full “all-singing and dancing” system for under $10k.
At the other end there are a number of packages that scale up to thousands of simultaneous calls- again these have a price tag to match. Expect to pay anything from $10k to $100k. For large carriers and PTT’s billing starts around $150k and goes north from there – the sky is the limit.
So, decide how much traffic you will realistically be running on your system and plan ahead accordingly. It may be a false economy to buy something cheap now if you are going to outgrow it in a few months and have to replace it.
If you let me know your projections I’d be happy to give you a list to start with of vendors to talk to.
Hope this helps.
Mat – email@example.com