In fact, it has tripled since July 2008, according to Nielsen.
18.3 million smartphone users accesed social networking services from their handsets in July 2009, according to analytics firm Nielsen.
That's nearly triple the 6.4 million people who were poking and tweeting from their smartphones in July 2008, which is a sign both of the increasing popularity of mobile social networking, and the wider increase in smartphone ownership.
Facebook attracted the most US smartphone users in July this year, attracting 14.7 million users according to Nielsen - 26% of all smartphone owners.
MySpace was some way behind with 7.1 million (13%), followed by Twitter's 4.1 million (7%).
"Social networking is probably the most important thing going on with mobile devices because the devices lend themselves to more social networking activities," says Nielsen's research director for technology and search Jon Stewart.
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"When you're not sitting at your PC you're not going to necessarily be Twittering about sitting at your desk, but when you're out and about in the world, you're more likely to have content and experiences that you want to share."
He clearly follows Twitter users with more self-restraint about tweeting their lunchtime sarnie than we do.
Nielsen has more stats on other kinds of mobile content, too. It claims 25% of US smartphone users used the Internet in July 2009 - which actually seems quite low to us - while 40% downloaded music, apps or games, and 7% watched videos.
