Not sure how accurate is the data but this seems interesting:
https://www.statista.com/statistics/1263720/mobile-messaging...
To call between France and various African countries in the early Android era, I remember first using Viber - but after a while everyone switched to Whatsapp in a few months: somehow, through some sheer black magic, Whatsapp had nailed voice quality over the lossy high-latency links that were the norms then, and users noticed.
Care to quantify that? PAYG SMS was/is consistently way more expensive than PAYG data[1] in every country I have visited; granted I haven't been to many countries, but I've visited most continents. IIRC, there's a 2-3 orders of magnitude difference in the costs-per-140-bytes sent.
Per WhatsApp message, which ends up being a few KiB per day for text only
Can't say people, to this day, have much of a culture of using whatsapp video calls. Skype was the majority in the Whatsapp takeover time and today it's a mix of Zoom and Skype. International calls also weren't that common.
So sounds like there may have been different motivations in your country than mine.
But I could jump onto coffee shop WiFi to negate that.
That theory would seem disproved by Mexico which is also pretty rural, but I believe their cell infrastructure sprung up pretty quickly and later than the US so "old school" sms didn't get the same traction.