I think iMessage is uniquely popular in the US since they all got hooked on SMS since their plans got "unlimited free texting" pretty early on, and iMessage is a mostly-transparent layer onto of SMS. Whereas in the rest of the world it was more common to be charged by the message so people adopted apps for "free texting". Also outside of the US it's probably more common to send international texts, which cost even more.
Not really, in Europe you have unlimited sms’ from like forever. Think people went to different platforms because communication was less clumsy and it was easier to do it also with Android friends. So all in one
SMS used to be an important revenue source for telcos. Basically they were charging for a best effort service on a signalling side channel. Free money.
Living in multiple European countries in the beginning of Smartphones (2007 - 2012) I can tell you that your experience is not universal.
In many countries carriers did offer unlimited sms plans, but they would cost a significant amount more over base plans which would say include 100 free texts a month. Also until EU regulations hit if you had any family or friends in other countries or ever went on holiday the cost of SMS was astronomical.
It took many carriers awhile to realize that "free" messaging apps were a significant threat, I assume because they were also charging heavily for data and just assumed because these used data they would make just as much money. Ignoring things like WiFi and how in the long run these apps would use such a small % of the data a user demanded they would be effectively free.
It's a very country-specific thing. In the Netherlands approximately everyone switched to WhatsApp long before unlimited SMS became the norm. WhatsApp was ubiquitous for years before Facebook bought them in 2014, but even 5 or so years ago my cheap monthly plan did not include unlimited SMS.
SMS fees are definitely the main reason a lot of people use apps today in Europe. They might not still be charging the same fees, but the damage is done.
The US phased out their SMS fees about the same time smart phones started to become popular. I think it was only due to regulation.
