Earlier quoted context omitted.
I have an iPhone (and macbook if that matters) and have no idea what all the rage is about. Is iMessage the default sms client? It's just called Messages on my phone. What does it offer? Mine looks like the stock android one. I see virtually zero options to do anything else than to send a message. Is it US only thing?
Messages sends SMS/MMS (on a Phone or configured Mac/iPad/Watch), but will transparently upgrade to the iMessage protocol when talking to another Apple user. This has substantially better features over SMS, including network access and the ability to send higher quality multimedia. If you don't ever want to fall back to SMS, you pick some other app (WhatsApp, Signal, etc). In the US, unlimited texting became a thing…
Namely: Telegram, Signal, LINE, WhatsApp, Discord, among others.
That is, all except one.
The one exception is, of course, Apple's iMessage.