The following commentary comes from an independent investor or market observer as part of TheStreet's guest contributor program, which is separate from the company's news coverage.NEW YORK ( Trefis) -- Yelp ( YELP) is one of the largest online business search, review and recommendation services. It competes primarily with Google ( GOOG) Places, Yahoo! Local, Angie's List ( ANGI), CityLocal and Gumtree. Yelp was also one of the third-party services integrated with Apple's ( AAPL) Siri voice-activated AI assistant, which was launched with the iPhone 4S last year. However, it has been integrated even further in the latest iOS 5.1 update, which was launched last week.