Sir/Mam
I can deliver two types of solution:
-Detailed plan to create your own SIP network connection, I will explain each component role and utility (without configuration).
-Useful information (links and details) to explore already implemented networks, paying services providers to use their networks(servers,routers,cables...) and start your own SIP service.
My first project in freelancer.com was a consulting about a network in rural areas so with that and my expertise I will be able to finish this project with great results in time.
I kindly ask you to seriously consider hiring me.
I will update the milestones depending on your choice of solution(I will not change if you want both solutions).
My best regards.