Group messaging is a service that allows mobile users to send text messages to groups of people and it works like a private chat room--only mobile.
The current popular players for group chat include GroupMe, Beluga, Kik and Fast Society. Google has now entered the market with a new service called Disco, which will act as both an online service and an iPhone app. Compared to the others, Disco is a bit more streamlined--offering fewer features but a simpler and faster operation as a result.
You might think it strange that this Google-owned messaging service is only for the iPhone and not the Android OS. The reason for this is due to the fact that Google did not build the application ground-up. It purchased the company alongside it's acquisition of Slide--an app developer for Facebook, MySpace and others.