Oh okay, I misunderstood its implementation. Still though, it will definitely not be any sort of SMS killer.
SMS isn't going anywhere soon.
Either way, I've never seen a breakdown of SMS usage by either category.
I haven't had a text plan on AT&T for many months, mainly because I use Beluga to send texts to my friends. iMessage is similar but much more seamless. I have saved hundreds of dollars by paying for the few text messages I still send/receive as I go.