Originally Posted by
aztimm
As far as I'm aware, any iPhone can use iMessage so long as there's an Internet connection. I know I've done it several times while on flights.
By the same token, someone could use WhatsApp or similar to essentially text through the Internet.
iMessage and WhatsApp are IM applications that run over the Internet. SMS is a service that uses public telephone network signaling and has nothing to do with the Internet. Apparently both are allowed on cell phone equipped flights. And some airlines limit or try to limit cellular or Internet voice calls, while other airlines allow it.