A recent study by Twitter looked at the behavior of people who mostly access and use Twitter through mobile devices, and found that they're quite a different bunch.
As you might suspect, primary mobile users are 57% less likely to use desktops for Twitter access than the average Tweeter. On the other hand, they're 86% more likely to report using Twitter via mobile devices several times a day. While smartphones remain they dominant means of mobile access, 15% of primary mobile users say they mostly use tablets for access. Demographically, the study suggests that primary mobile users tend to be younger, but there seems to be no gender differential.
The biggest differentials are in how primary mobile users make use of Twitter. They're more likely (than the average Twitter user) to use Twitter when they wake up (157%), and when they go to bed (129%). They're more than three times more likely to use Twitter during daily commutes, 160% more likely to Tweet during work or school, 169% more likely to Tweet while shopping, and 301% more likely to Tweet just before or after watching a movie, and 32% more likely to Tweet while watching TV.
They're also 62% more likely to communicate with people near them (trading locations or sharing a photo).
I'm not surprised - mobile is opening new opportunities for communication and information access, and we're seeing changes in how people access and use information. Mobile is also continuing its growth globally. According to the ITU, more than half of all mobile subscribers use smartphones and/or tablets as their primary device, and more people access the Internet through mobile devices than through land lines. There's a strong potential for mobile to be a transformational technology, changing the way people access and use media and media content. Media need to track, understand, and take advantage of those changes to remain successful over the long term.
Source - New Compete study: Primary mobile users on Twitter, Twitter's Advertising Blog
Edit - Cleaned things up a bit. (2/20/2013)