Popular online business review site Yelp announced an updated iPhone app today which expands upon its recent addition of check-in capabilities, placing them in direct competition with the likes of Foursquare. Previously, Yelp users could check in at business establishments while also viewing or creating a review of the location. Today, the service is adding "Yelp Badges" to the app, as well as the opportunity for users to attain "Royal" status at any location - both clearly interpretations of similar features found in Foursquare.

Yelp Badges will work in the same way Foursquare's do, but Yelp says "it's up to our users to figure out how." As for crowning royalty, Yelp is taking a medieval approach to Foursquare's mayorship feature. If a user has the most check-ins at a business, they are bestowed with the title of Duke or Duchess. If a user racks up enough of these titles in a specific neighborhood, they become the Baron of that area, or the King at the city level. It's an interesting spin on the "champion" model, but it's not necessarily ground-breaking innovation as far as check-in gimmicks go.

So why is Yelp going to the trouble of adding these Foursquare-inspired features? While they recognize the popularity of other location-based apps and want a piece of that pie, they are also attempting to leverage high mobile traffic for their service. According to the company, 27% of Yelp searches and over 500,000 calls to businesses each month month (or 1 every 5 seconds) originate on its iPhone app.

While their main goal seems to be aiming resources at their mobile users, can Yelp also compete with Foursquare? With this latest update, Yelp now mirrors Foursquare's functionality, but the one thing Foursquare currently has is business partnerships for special check-in coupons. If they tried, it would seem likely that Yelp could accrue similar deals, and their review and rating functionality could actually tip the scales in their favor.

Gowalla, a simlar popular check-in app, doesn't feature mayors, kings or masters of the universe, but does rank user check-ins at each location. Yelp says it has pushed the update to Apple, but it has not yet been made available for download, so keep an eye out for the app in your upgrade section on your iPhone or on iTunes today. Not an iPhone Yelper? Check back here later for screenshots once the app is live.