After enabling the feature via the settings > lab list, you scroll to your contact, type in their mobile number and text via the IM box that pops up.
Friggin' awesome! And this from something that still is in â€œBeta.â€
Implications - With that being said, there is likely lots of cool stuff coming from Google in the next little while. For those who like to stay totally tapped in to the world of online media, don't dare take your eyes off Google!