Strategypage has a post on the cellphone revolution: read the whole thing. A lot of it is about why cellphones are everywhere, and then they go on to note how this has changed war by changing the way you gather information. (i.e. pissed off civilians can now report where the bad guys are hiding).
of course, it also allows the bad guys to post misinformation, and I won't even go into Trumpie's twets, which are taken literally by the press who hyperventillates, but we ordinary folks recognize he is trolling the press, and just laugh.
well, anyway, SP notes that 5 billion people now have a cellphone, and modern cellphones are in effect mini computers. Landlines are expensive, but put up a tower and voila, instant coverage... and texting is cheap even for the poor (here, you can buy a "load" for 25 pesos, i.e. fifty cents, and do a lot of texting to your friends and family)..
I got my first cellphone in 1988, and was amazed when I visited the Philippines in 1991 and saw a sign in the village near our farm: Cellphone here: Calls to Saudi available.
And my friend in Africa has had one for about six years, so I can now send her money via Western Union and she can pick it up quickly instead of waiting three weeks for the snailmail for the number so she can pick it up.
and of course, cellphones are mini banks and let rural people buy stuff on line (which is why Jack Ma and AliBaba is so rich: he has revolutionized how rural Chinese buy stuff).