Yelp has had lots of success with its iPhone app, which currently accounts for 5 percent of its overall traffic. This is partly because its base of urban “foodies” maps well to iPhone user bases.

This was a smart platform choice — a key issue for small companies given device and OS fragmentation, combined with finite development resources. I spoke with Yelp’s Sonia Survashi McFarland last week about lots of these development issues and am working on a longer report on this topic now (stay tuned).

The other thing we discussed was mobile reviews. Yelp has long shied away from letting users write reviews on the go — mostly because it compromises the quality and integrity of the long-form reviews that have come to define the site (see my conversation with Yelp CEO Jeremy Stoppleman a while back).

Partly due to user demand and partly (my speculation) from seeing the success of mobile reviews generation from Citysearch and others, Yelp will launch a new set of features for mobile reviews generation. BUT, this will be done in a way that walks a fine line between mobile content generation and avoiding the cannibalization of its online reviews.

The integration is pretty clever and should serve to generate more reviews online. One feature lets users “draft” a review by letting them enter a star rating plus any words or menu items that will help them remember the experience. This is saved and can be expanded and published next time they’re back at their computers.

But the main features of the new UGC integration are more customized for the mobile experience and seem to follow the trend toward micro-blogging made popular by Twitter. Here the “twitter versions” of reviews can be written (140 characters or less), which Yelp is branding as Quick Tips.

This separate designation allows it to use these micro-reviews in different ways and in different places than its core (longer) online reviews. The Quick Tips, for example, are presented more to mobile users than online users. Online, they’re also separated from longer reviews. This is similar to what European social local site Qype is doing (see our conversation with them here).

It’s also following more of a social networking mold by allowing users to see a Facebook-style news feed of events, reviews and Quick Tips happening all around them — both from the community at large or from the friends they’re connected to on Yelp. See a video that walks through some of these features here.

UGC should be a natural extension of the mobile use case and also a natural evolution for the many online local search sites that are developing mobile products. Expect more announcements about mobile local reviews very soon (hint).

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Images care of TechCrunch.