I have recently came across this new (unless I was asleep for last few months/years) product called Pay Per Call. Very intereting idea. As a former real estate agent I can appreciate a product like this one. In real estate as well as in some other industries a transaction does not take place on the website, therefore while pay per click advertising helps, this new product can bring a new edge to professionals who generate their leads via telephone.
Details for affiliate program can be found here.