Developers around the world have been building new sites and retrofitting existing ones for use on the iPhone, and the social networking site Facebook joined the fun. To see what Facebook on the iPhone looks like, check out this slideshow posted to Flickr by Citizen Agency's Chris Messina.

Facebook for iPhone is smartly designed because it keeps things simple. I found that you can perform most of the tasks you'd normally do during a normal Facebook visit (checking mail, checking up on friends, approving new friends, etc) easily on the iPhone. The four parts of Facebook you use most--the Home, Profile, Friends, and Inbox pages--are organized in tabs across the top of the page. This helps you get to the stuff you need with just a touch or two; this is important because mobile bandwidth isn't always predictable. On a purely aesthetic level, Facebook for iPhone manages to retain much of the clean, uncluttered look you notice at the desktop browser version of Facebook.

Response from tech bloggers and discussion board posters today has been almost completely positive -- Michael Arringtonat TechCrunch called Facebook the best iPhone-optimized app yet.

The buzz over mobile social networking has been going on for awhile now, but actual user numbers remain low. M:Metrics released new research Tuesday saying that only 3.5 per cent of US mobile subscribers (7.5 million) accessed social networking sites during June. The firm says Facebook’s mobile US audience is about 2 million, and is made up of mainly college-age users.

Still, a lot of people believe that mobile social networking is going to be huge, especially as faster wireless networks become available. Meanwhile, mucho venture capital continues to flow into mobile social networking tech in its many forms.

What is it about mobile devices and social networking that make them a match made in heaven? Is the urge to social-network so strong that we simply can't wait to get home to do it? Or will new mobile social networking services simply do things that static, desktop-based sites cannot? Will mobile devices take social networking to a whole new level? If the future is really "unwired" and "always on" as they tell us, then people will demand it.