To kooper: I am not sure if I understand you. If you buy a billing solution, this is normal that you put it on your VoIP network and collect data from gateways from around the world (this is what we are using). Or do you mean the hosted billing solution? I know there are people who are doing this, and it is really to accomplish (you can have unlimited number of virtual environments on your installation) – but we are using our own billing instance. Contact them, they probably have some hosted billing offer.