The main draw of these devices does appear to be telecomm; the Pew article is from 2018, so the numbers have probably changed by now, but back then the majority of users were using dumbphones. I can remember watching videos as early as 2014 showing nomadic tribesmen in Africa using flip phones for mobile payments.

I was under the impression that these devices were Wi-Fi enabled; I take your point that penetration rates for broadband were nowhere near as high back then, but I still think a lot of the criticisms were misplaced. The penetration of telecomm into these countries is going to have massive upside in the next two decades, and computer literacy plays a part in that. I suspect there are compounding network effects involved here that don’t really exist for linear problems like healthcare (though I could just be underestimating the immediate benefit of $1 in medicine vs. $1 in digital literacy).