I can say, excellent idea and I hope that it goes well for you. I have an iphone and can see exactly what you are trying to do. Would definitely lighten the load.
On the other hand, just because someone doesn't google chat doesn't mean they are behind the times. Its just cheaper for me to have a family texting plan then it is to have a data plan for my family. 20 a month for unlimited texting is a hell of a lot cheaper then paying for a data plan for each. besides my Iphone is second hand so I didn't have to get a data plan for that either. I can still use all the apps that apply when I need them. Best of luck with your app, and if it comes to apple, I may have to look into it, but no reason to insult for a lack of technology.