Comment by kalleboo

I think iMessage is uniquely popular in the US since they all got hooked on SMS since their plans got "unlimited free texting" pretty early on, and iMessage is a mostly-transparent layer onto of SMS. Whereas in the rest of the world it was more common to be charged by the message so people adopted apps for "free texting". Also outside of the US it's probably more common to send international texts, which cost even more.