Somehow, Android’s messaging mess is about to get even worse
theverge.com
theverge.com
I'd consider SMS as an "app" too, with the limitation of no group chats, and requires a roaming SIM card if you happen to go abroad.
Out of the examples you listed, personally, I don't use FB properties (so no WhatsApp or Messenger), nobody here uses WeChat/Line, Telegram is gross (hard pass on closed source faux-secure messaging), and I've never even heard of Viber. But I use Signal, and it's integrated with SMS (in the Signal app, it'll use Signal to talk with other Signal users automatically, and fallback to SMS otherwise).
And yeah, SMS is basically free (read: unlimited usage included in pretty much every phone plan on every carrier) in North America.
And it should be. As I understand it the messages are sent as part of the usual cell tower polling messages with no overhead for the network (Which is why they're length-limited).
Though I would expect that to change pretty rapidly once gen z is in the ascendant. I don't think they use SMS much, a lot more Instagram messenger than anything it seems like.
One of the reasons I threw away my iPhone was because I detest iMessage. I'm not sure why the author thinks that was the way to go.