So this is a shot across the bow at WhatsApp and kik and MessageMe right? Those apps are incredibly popular in developing nations.
WhatsApp and the like didn't invent mobile messaging, they just went through the trouble of building J2ME clients across all the cheap handsets found in the developing world so that mobile messaging was available across all devices. Facebook isn't going to make any dent at all in the developing market unless they do the same.
That said, Android is getting so cheap that it is turning into a chasm between totally dumb phones (not J2ME, just a simple handset) and Android. The former is still the vast vast majority.
The thing is that many of these apps are both pretty good, and have insane market penetration... It's hard to see why anybody would switch to a FB app that's very likely worse if they're already using something else (so all their contacts are there).
LINE, in the meantime, just celebrated its 300 millionth user, and its user base is concentrated in Asian countries.
I seriously hope it doesn't cause any issue for these companies, I've just got back from a few months travelling and Whatsapp was invaluable.