In Google's model, users click on an icon of a phone, and then enter their own phone numbers, after which Google calls the users and then connects them with marketers.

Google's entry into pay-per-call could create momentum for the nascent market, said Kelsey Group Analyst Greg Sterling. "It's another indication that calls are going to be pervasive as an offering side-by-side with clicks," he said. "If Google adopts [pay-per-call] and Yahoo! adopts it, then obviously that's a huge potential marketplace opening up, and advertisers will adopt it."

He added that the move could contribute to Google's continued growth. "The margins you can get for a call are much higher than those you can get for a click, and certain advertisers are willing to pay that premium."

Marc Barach, chief marketing officer of major pay-per-call company Ingenio, agreed that Google's entrance was good for the market. "In the big picture, I think that greater adoption is good for the entire industry--pay-per-call is a nascent industry; there are only a few players," he said. "To get a player like Google--that's fabulous."

Barach added that Google's interest in the pay-per-call model shows that phone contact is becoming integral to e-commerce. "What's interesting about this is that it's further proof that voice is a fundamental part of e-commerce," he said. "The fact that most of the major companies--Google, Yahoo!, and Microsoft--have all started to move into the VoIP arena [shows] the writing's on the wall."

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