Hosted / cloud telephone provider who charges per call path?

[thefreeaccount]

Are there any hosted / cloud VOIP telephone providers that charge per call path rather than per extension? It seems to me that the hosted provider is ultimately paying expenses per call path, so this should be a viable business model. All the vendors I've been able to find want to charge per extension along with some kind of "unlimited" calling plan, which seems like a huge waste of money unless all your employees do nothing but talk on the phone all day.