Pay per call is not something that Yelp currently sells, to my knowledge. However this little bit of data caught my eye in a Yelp blog post last week:
Last month, over half a million calls were made to local businesses directly from our Yelp iPhone App. That’s about 1 call every 5 seconds to a business as a result of Yelp.
Imagine if Yelp were to start to monetize these calls. There are several challenges in doing that of course (e.g., they’d be intercepting calls going to those businesses arguably anyway). But the volume suggests the company has an opportunity with PPCall.
And when other smartphone platforms are included the call volumes could approach a million monthly calls.
Related (though nothing about the data above): Mercury News interview: Jeremy Stoppelman, Yelp CEO