While I can't comment on the third world in general, I saw a lot of solar cell setups for charging cell phones in South Sudan - people even ran solar charging as a business; a solar panel, some car batteries, a black box of electronics and 3 to 5 South Sudanese pound for a full charge.
Also saw plenty of cell towers with solar panels and battery banks, with diesel generators for backup. Not as clean or tidy as plugging into the grid, granted... but it works. Was a life line for me for a year spent down there, and twice so for the people who lives their whole life there.
Just because you can't plug something into a national grid, don't mean you can't get power... often cheaper and more reliable than the grid too - at least in Juba.