Loopt (UPDATE)

 - Jun 10, 2008
References: loopt & news.cnet
Loopt, the "social compass" that transforms your phone into a pinpointing device to show you where your contacts are at any given moment was just demonstrated on the iPhone at WWDC. The GPS application will be free for iPhone users, enabling them to track their friends, via pinpoints on maps, in real time.

Loopt will be available as soon as Apple's AppStore launches, along with other applications by Sega, eBay and TypePad.

Loopt is already available on the Blackberry, as seen in the demo above.