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Pressure grows on Apple to open up iMessage
(finance.yahoo.com)
This is a most excellent place for technology news and articles.
I have to say that in Denmark at least, iMessage seems to thrive quite well. There are quite a lot using Facebook messenger, but SMS and iMessage is a close second. This is entirely from my point of view. Never met anyone using the examples you mention, unless they are communicating with foreigners on a daily basis.
In finland everyone I know uses WhatsApp, and my friend circle and family also use Signal. So, eh.
It's popular in Sweden too