Ingenio has released an application programming interface (API) for its pay-per-call technology, allowing interactive marketing agencies, search engine marketing firms and third-party technology providers to enable and manage pay-per-call advertising campaigns for their clients alongside pay-per-click campaigns, reports ClickZ.

The API provides ad creation and geo-targeting, auto-scheduling, customizable reports, and real-time visibility into the advertiser's competitive bid environment. Developers can also use it to create and customize new applications around the campaign data.

Ingenio's pay-per-call ads are distributed on networks like those of AOL and Miva; other distribution deals are apparently in the works. Advertisers bid a per-call price they will pay for phone calls resulting from the ad. The average bid price is $6-8 per call, depending on keyword.

"Pay-per-call is a perfect example of the 'reverse direct marketing' paradigm shift that's going on, where the prospect is seeking the business," said Sara Holoubek, chief strategy officer at icrossing, which has has been running pay-per-call campaigns for a few clients.