"Apple today released a beta version of Messages for OS X. The application takes over for iChat and allows Mac users to send instant messages to iOS users."
I downloaded and tried this out today, works pretty slick. If you prefer to read your walk through versus watching it on YouTube above, then head over to MacLife where they have done a first look of the new program from Apple.
iPhone 4, 1.6 GHz Core 2 Duo MacBook Air, Apple TV, 2.66GHz Intel C2D Mac Mini, 1TB TC, Airport Extreme,several iPods and an iPad, 32GB Wi-Fi version. Follow me on Twitter.