We just released a new version of Navizon for iPhone that can run in the background. With Navizon you can now see where your friends are right now, as opposed to where they were several hours ago (which is the case with most Location-based applications that send your location only when you launch them).

This new version also includes MobiFindr, a feature that lets you locate your iPhone just by sending an SMS to it (very convenient in case you lose your iPhone).

More details on this new version are available here.