Ingenio Chief Marketing Officer Mark Barach said the partnership with InfoSpace adds around 300 million queries per month to the company's existing network of one billion monthly queries; the other major distributors of Ingenio pay-per-call ads are AOL and Miva. InfoSpace also serves pay-per-call ads from startup Jambo--a deal that was inked in late October.

Barach said that the partnership with Infospace shows that pay-per-call is gaining momentum as an ad medium. "We're starting to see the tipping point and beyond." he said. "There is a sea change in the readiness in the marketplace for this kind of offering."

Major Internet players are also getting into pay-per-call--search giant Google began hosting click-to-call ads into its local search results as a test in late November--and, Barach said, Yahoo! has been testing pay-per-call with Ingenio.

He added that moves to embrace pay-per-call can be viewed as part of a larger interest in voice on the Web. "There's more movement around voice, in the really big picture," he said, citing eBay's recent purchase of Skype, in addition to Google and Yahoo! tests of click-to-call. "It's now undeniably a trend. Voice is a very important part of e-commerce, and the Web has been mute for too long."

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