Utterly redundant post. I am fully aware of this, having used iphones since the inception. Anyway i was merely pointing out imessage only dominates in the US market and everywhere else its imessage, not what its limitations are.
I just explained to everyone WHY people use it rather than WhatsApp. Most people in other countries use WhatsApp, Line, and WeChat etc... because those countries charge for text messages. Otherwise, as a messaging service, they are definitely inferior to iMessage/SMS because they will fail when servers go down and/or no they have no Data connection by nature of their reliability.
Whether this post was useful to YOU or not is utterly redundant. I simply helped people understand why the US uses iMessage and Text Messages. US Carriers don't charge for Texts and iMessages usually cost very little data.