CitySearch, producer of online consumer city guides (and a subsidiary of InfoCommerce Group's latest favorite, InterActive Corporation), has raised eyebrows with its announcement that it will be offering advertisers a pay-per-call option, in addition to its existing pay-per-click programs. Pay-per-call is analogous to pay-per-click, but the mechanism for capturing and measuring ad effectiveness is phone response rather than clickthroughs. Advertisers run a special number in their online advertisements, each call is tracked by the service provider, and the advertiser pays based on the number of calls received.What's going on? What we're seeing is increasingly explicit acknowledgement that -- gasp -- clickthroughs are not the same as sales. The great irony here is that the place where pay-per-click advertising apparently doesn't resonate is among smaller, local advertisers, so-called "unsophisticated advertisers" who view pay-per-click as buying increased traffic, not increased business. CitySearch believes, and we concur, that, when it comes to pay for performance, it's a lot easier to prove the value of, and charge for, forwarded phone calls than anonymous clicks. And while it may seem hard to believe, a large percentage of businesses still don't have Web sites, but pay-per-call can work for these companies, while pay-per-click can't. Pay-per-call combines the best of two worlds - the increased reach of the online media, the traditional measurability of direct response and the siren song of "pay for performance." And it proves the significant benefits of viewing old world and new world marketing channels as complementary rather than competing.While the CitySearch embrace of pay-per-call is significant, real credit for this important development properly goes to FindWhat, which launched the concept back in September. FindWhat is working in partnership with technology provider Ingenio; CitySearch is using technology from CIRXIT. This new technology is already hard at work chasing the huge B2C market, though we would contend the opportunities are just as big in B2B. Unlike the consumer market, B2B buyers are not known for purchasing machine tools, overhead cranes and printing presses through online shopping carts. B2B purchases are typically more complex, with longer sales cycles. At some point the buyer usually picks up the phone to call the seller. That's why showing true return on investment is so difficult for those selling pay-per-click programs to B2B companies. A pay-per-call capability is a much more apt and convincing selling tool for B2B publishers.So keep your eye on pay-per-call. For B2B buying guide publishers, this is one killer app that can actually live up to its promise