Citation needed; I'd certainly love to know whether J2ME devices were a significant chunk of WhatsApp's actives, but there's zero data to back up the suggestion..
From my personal experiences, international countries that have smartphone adoption use Viber, and the feature phone countries use WhatsApp.
WeChat - china
S Korea - kakaotalk 90% market share
LINE - Japan 50 million users with 300 million worldwide
And all three have significant revenue in double digit US millions a year, unlike WhatsApp which has no real revenue...
So, WhatsApp is definitely used in high-profit markets as well.
Source: http://www.nu.nl/tech/3506473/whatsapp-heeft-kwart-miljard-a...
WhatsApp users are mostly not early adopters like you and your friends. They are ordinary people, because WhatsApp is is a simple communication tool targeted to everyone. And that's why they keep doubling their user base.
It has basically replaced texting. Even my mom use it, which for me it's the definition of "wildly popular".
As far as I know, both are very profitable through sales of digital goods like stickers etc.
That's what made me return to WhatsApp in the first place. That, coupled with an apparently flawless experience.
There are about five or six odd people in my life (professional or private) that I message frequently. Even if 1 out of them isn't on a particular messaging platform, I can't adopt that platform wholeheartedly. With Fb Messages, Hangouts and every other popular smartphone oriented messaging platform there would always be that one or two contacts that you regularly communicate with, who would be left out due to having an incompatible device. Whatsapp on the other hand works on pretty much every phone. When you want to replace something as prevalent as SMS, the long tail matters.
There's another tangible benefit of focusing on so many platforms. Whatsapp, which doesn't spend much (if anything at all) on promotion, is prominently featured in the advertisements of many budget phones, as manufacturers see Whatsapp support as a strong selling point.