Social review service Yelp has snuck the first Augmented Reality (AR) iPhone app specifically for the US into the iTunes App Store. The undisclosed new feature allows iPhone 3Gs owners to shake their phones three times to turn on a view called "the Monocle." This view uses the phone's GPS and compass to display markers for restaurants, bars and other nearby businesses on top of the camera's view.

Blogger Robert Scoble discovered the hidden feature and posted about it on FriendFeed today. A screenshot is below.

See also, from 1 hour later: The Wall Has Fallen: 3 Augmented Reality Apps Now Live in iPhone App Store

Right: Blogger Josh Bancroft is surrounded by Yelp-reviewed businesses when he looks south.

Developers did not expect to be able to get Augmented Reality apps into the App Store until the release of the next iPhone OS this fall. Earlier this week, though, we reported on what appeared to be the very first - an update to an app called Metro Paris Subway.

Layar and Wikitude, two European companies offering multi-purpose AR browsers, both have Android AR apps that include content for the United States, but neither company has released an iPhone app yet. Layar's CEO said yesterday that he was testing an iPhone version of his company's software and that it was "very fast."

Building a little AR into an already established app seems to be the method of choice for sneaking AR into the app store.

The best use case for this Yelp app might not be for finding businesses out of sight, but for pointing your phone at businesses you are physically near and discovering Yelp reviews of those places.
Yelp had already built a layer of data for AR displays that it deployed on the Layar platform. Having done that, it was probably relatively trivial to build its own AR feature. Correction: AR company GoWeb3D says it actually built the Yelp layer for Layar using the Yelp API and with Yelp's blessing.

This may be what the future of mobile Augmented Reality looks like: many vendors offering their own in-app AR views, and a handful of AR browsers like Layar, Wikitude and Acrossair aggregating many different published AR views or layers.

Thanks to Steve Garfield for the demo videos above.