> Since iMessage is the default messaging app, few iPhone users bother installing anything else. Moreso, there's no such thing as a default messaging app, just

> Since iMessage is the default messaging app, few iPhone users bother installing anything else. Moreso, there's no such thing as a default messaging app, just like there's no default phone dialer. The system handles telco messaging and calls. But there's also no real limitations elsewhere as long as you aren't requesting SMS/MMS specifically. I can send an image to someone via Signal just as easily as I can via iMessage - they show up in the same lists. This is different from cross-vendor standard protocols like email, where you may want a mailto: link to compose a mail in the app the user actually has configured. For mail you can configure a default application.