sms is fast and easy
I can send out an IM on Whatsapp in a millisecond. It has a chat style layout. I can see if the recipient is typing, online or asleep. I can send pages of info or pictures etc. They will get it instantly and not in 4 hours or so as I found on NYE with my SMS's. It alerts me in a similar way to an SMS as well. I see absolutely no advantage to the old methods apart from that it is a 'standard' across most phones. SMS will die. No doubt about it.