How does SAS connect to standard telephone networks?

I have been puzzling over how SAS nano-satellites connect to standard telephone networks. In the Sept. 5^th SAS announcement of the first voice, text message and image exchanges it said:
Along with enabling a voice call, the 3 Diamonds nano-satellites, which Sky and Space Global launched into space in late June 2017, have also demonstrated their capability to facilitate the exchange of text messages, voice recordings and images between different users. As part of this process, SAS has successfully tested the "store and forward" capability of its technology, which includes sending a message to the satellite, keeping it in satellite memory and downloading it to a receiver.
It's not clear from this whether this is between two satellite enabled phones or whether it involves some sort of base station, which in turn connects to standard mobile networks or fibre / copper networks. I imagine that for users of the satellite enabled phones to fund their calls and for SAS to get its cut, there must be some route to credit card payment systems. I know that bitcoins and such like have been mentioned as means of payment, but that would seem to be a step too far for societies which are isolated and lacking in sophistication. It would be a step too far for me!

Also, if there aren't connections to standard networks, calls will tend be limited to those within sparsely populated areas, which would be a major limitation in terms of the development of such areas. To provide full coverage throughout the subequatorial region i.e. access to all possessors of a phone, there would have to be a fair number of "base stations". Who's going to build and fund them and at what cost?

Apologies if these issues are well understood by others and it's just that I've missed the key threads amidst all the chatter about the share price!

Chris