Someone earlier today asked me for a list of the top mobile social networking sites. This prompted a deeper question on my part. Exactly what is mobile social networking?This question is not as easy to answer as it might seem. Social networking is pretty well defined on the desktop. From LinkedIn to MySpace to Facebook, the object of all social networking sites is pretty much the same: Build a list of your friends then use that list to meet new people and expand your network. In short, social networking is about finding new people.

On the mobile Web, though, this isn't as easy. The mobile Web is not great for exploratory tasks. Most mobile applications are either peer-to-peer communications (i.e. texting or push e-mail) or, as Google keeps stressing with its mobile applications, quick hits of data.

As a consequence, social networking on mobile devices looks a lot more like messaging with presence and location than it does on the desktop. Mobile social networking seems, at least for now, to be more about meeting the people you already know.

Social networking sites like Dodgeball are designed specifically for this purpose. Other social networking sites like Twitter or Jaiku are designed to let your friends know what you're doing with quick bursts of information.

Yes, I know many people categorize Twitter as a micro-blogging site and not a social networking site, but they're wrong. Just take a look at TwitterVision. The content updates on Twitter look a lot more like the friend posts on MySpace or Friendster than full-blown blog posts.

But, back to the subject at hand. Mobile social networking will evolve into something different than its desktop parent. It will continue to be more about messaging and presence and less about finding new people or building networks. And mobile access to desktop social networking sites will follow a similar path.