Sure people use a variety of messenger apps, Whatsapp, Messenger, Instagram, Telegram, Signal, Snapchat. Since you don't have a guarantee that any one person is using this or that the default messaging app (Messages on iOS, whatever it is on Android) SMS is the safest bet that always works. That's typically what people use when they get someone 's contact: hand over phone, ask to type number in focused input field, send $firstname SMS; bam, handshake done.
> WhatsApp has >50% market penetration there
Lots of people here have WhatsApp. Doesn't mean it's their go-to, they still don't ditch SMS[0] nor dunk on "green bubbles". And then if both parties have an iPhone it just so happens that they obliviously converse over iMessage as a side effect.
[0] Except for group chats. But then they just create groups in whatever's at hand, which may or may not be WhatsApp. And that's mostly because SMS group messaging is thoroughly broken (as in it works more like email than IRC and people want the latter). But for 1:1? SMS is brutally consistent.
So there's often motivation to install your country's dominant messaging app beyond just the cost of SMS.
If they were expensive, users jumped ship right away. If they were nearly free, people just kept using them on brand new devices as there were no compelling enough arguments to switch.
To answer your question more directly, Sweden comes to mind.