[Skunkworks] Seeking advice on GPS-enabled phone

Hi, I plan to map some health facilities in Mandera and I need advice on your experience with mobile phones in getting GPS co-ordinates/locations. I am assuming mobile phones depend on the infrastructure of say Safaricom to get the GPS locations. What happens in areas where there is no network, how will I get the GPS co-ordinates? Finally, in your experience, what particular phone model has worked for you; what would you recommend? Thanks James