Axel this was a very good post and I agree with all levels of the requirements. Your assumption that the network doesn't work might have a flaw, CWID seemed to have no problems with the function. That means that the local user was serviced, context switching took place, the back haul happened. I saw the StrateVoIP billing system two years ago at the SHM. It was a bit crude but very functional. Online subscription seems to be availvable from multiple sources.
The real sticker would be the context switching anyway and that seemed to work at CWID. If they are using a Linux kernel as described in earlier information, finding a real time programmer shouldn't be difficult. So what is your concern?