Bango is a uk company I think they have been around since 1996. They have Direct Carrier Billing markets in varous locations around the world including Australia.(telstra was used in one of their examples).
Bango.com has more details about the company and has links to their investors page and plenty of info on their DCB penetration rates and so on.
I have to say their website is quite simple and easy to understand. (I think mbe needs to do a better job of this).
Looks like Bango managed to land DCB in the United States by acquiring 'billtomobile' just recently (May 2016) for 3.5 million.