These problems frequently need to be tackled from multiple angles.

I recently heard about a company called Endaga who have come up with a single box that you just plug in to the power and an internet connection, and it creates a small-scale “cellular” i.e. mobile network, which then makes VoIP calls to the outside world. They’ve based it on OpenBTS, and they’re selling it at just $10k, with Endaga taking care of almost all configuration, interconnect, etc. They’re pitching this at rural areas in the third world where mobile coverage is sparse or non-existent. Obligatory link.

Note: I have no connection with Endaga, etc.