This week we're running a 5-part series of posts looking back on the significant trends of 2011. Today we're reviewing group messaging, the hot trend at this year's SXSW festival. Group messaging started out as a battle between several startups, but over the past few months it's turned into a fascinating Google vs. Facebook vs. Microsoft faceoff.

Group messaging threatened to become a breakout activity at SXSW, as tweeting and 'checking in' had done at previous SXSW events. It didn't quite pan out that way, partly because a giant (Facebook) acquired one of the leading scrappy startups before things got interesting. Also, there were minor but irritating glitches with the apps. A few months on and group messaging is no longer as hyped as it was at SXSW. Yet it's more than ever a key feature in the social and mobile products of Google, Facebook and Microsoft.

What is group messaging? It's real-time and asynchronous communication between groups of people. Which these days typically means via your mobile phone. In many of the apps we'll discuss below, messages are received as an interruptive SMS or push notification.

The SXSW Battle of Group Messaging Apps

Cut to late February 2011. A couple of weeks before SXSW Interactive, the biggest Internet technology event of the year. Many people are licking their lips in anticipation of the upcoming battle of the group messaging startups. Beluga vs. GroupMe vs. Yobongo vs. Kik vs. all comers!

And then Facebook goes and ruins it all by acquiring Beluga before a SXSW shot has been fired.

Beluga and GroupMe ended up the most popular of the group messaging apps in Austin, however neither caught on in a big way.

Enter... Google Plus

We mentioned yesterday that Google Plus, the new social network from Google, has forced Facebook to re-evaluate its privacy options. Google Plus has also upped the ante in group messaging.

Google Plus has two excellent group messaging features. The first is a group video chat feature called 'Hangouts,' which got a lot of attention on launch because it enables up to 10 people to participate. The second feature is much more akin to Beluga and GroupMe. It's a mobile-only group texting feature called 'Huddle.'

Facebook Responds... But Where's Beluga?

Just a week after Google Plus launched, Facebook announced its own video chat and group messaging features. The video chat part is powered by Skype, but it's limited to one-to-one video chat (so it's not a 'group' chat feature).

Facebook's group messaging feature is likewise underwhelming when compared to Google Plus. It's not available on their mobile apps, for a start. Also it's limited to chatting with official Facebook 'groups' (which aren't very well used, because they're a user experience mess) or by going through some unintuitive steps in the Facebook chat interface. In short, Facebook's group chat is badly designed.

Where is Beluga in all of this? So far nowhere to be seen. Ironically, there are reports of technical problems with Beluga on its Facebook Page. One assumes Facebook will integrate Beluga at some point though - surely it has to in order to keep up with Google.

We should also mention the group messaging functionality in Windows Phone 7, Microsoft's latest mobile offering. Its "People Hub" enables you to chat with groups of people, much like Huddle does.

What is Your Favorite Group Messaging App?

Overall, it's been a fascinating year for group messaging. It started out as a battle between several tiny startups, but by mid-year it's turned into a battleground for the big guns: Google, Facebook, Microsoft and others. Let us know your favorite group messaging app in the comments!