I think facebook did a great job with their Messenger app. Most people are on facebook already (so the no sign up sales pitch isn't very convincing), it's available on almost every smartphone (and not just a particular brand like Blackberry Messenger), most tablets and with every computer connected to the internet. Probably even on some TVs (?). It's a cheap substitute for text-messages. The app is really simple and looks good.

Competing against them is a waste of time.