When Apple announced the addition of a compass to the iPhone 3GS, shortsighted onlookers responded with a yawn. Yay, we can find magnetic north.

But iPhone app developers quickly saw an opportunity, and a new breed of "augmented reality" apps are about to be born.

Holding the phone in front of you, locations are plotted on a live view of the world in relation to where you're standing. The apps combine the phone's key features -- camera, GPS, compass and Internet connectivity -- to create a sort of heads-up display reminiscent of first-person shooter video games.

The first two poised to hit the App Store -- pending Apple's approval, of course -- are Nearest Tube, which plots subway stations in London, and TwittARound, which shows nearby Twitter users.

Nearest Tube overlays information about subway stations, including the stop's name, its distance from your current location and which lines it serves.

The first version of the app, which has already been submitted to Apple, will cost $1.79 per city and will ...