First of all, we're talking about modern IM built into smartphones, not AIM garbage. Google Talk is still a viable platform that simply needs improvements in order to work better for people. It's already built-in on most people's smartphones since Android is the top-used platform right now, so all Google needs to do is make it more like iMessage and it will be used even more than it is today.
I dunno about you, but GTalk is the still one of the main ways people chat today simply because its built into Gmail, so just powering it up with iMessagey features is all that is left to make that platform great.
Second, IM is not dead. Look at people's enthusiasm for iMessage, Whatsapp, Kik and BBM, all forms of advanced IM. That's what people REALLY want instead of a dinosaur like SMS. You thinking is simply backwards, IM isn't the past, its the future, and the success of these platforms shows that. The only thing getting in the way are carriers.