Online advertising coordinator Marchex is expanding its partnerships to enter the mobile search space, says COO and President John Keister.

“Interest in the mobile space in the last 12 months, it’s gotten greater and greater because the monetization strategy is becoming more important.  It’s not just delivery content,” Keister said. “We think the mobile opportunity is really in the beginning stages as far as advertising.”

Now, Marchex’s new partners include AdMob, Ringleader Digital and 4INFO. AdMob is a mobile advertising service; Ringleader Digital specializes in tailoring advertisements by device functionality; and 4INFO works in SMS, officials explained.

All three partnerships begin “effectively now,” Keister said. “Obviously, Google made a huge market out of the desktop PC … the question now in the mobile world is who’s going to own the mobile networks and drive that value? We’re sending tens of thousands of local ad campaigns to Google on a monthly basis,” he added – Marchex works with Yahoo too, so the lines between cooperation and competition are blurred, he explained.

In addition to acquiring and placing local online advertising, Marchex last summer acquired VoiceStar for about $28 million in cash and investments. VoiceStar provides call tracking and reporting services so advertisers can measure their results and was just starting to look at the mobile business when Marchex bought them. The new mobile partners will use this service as well.

Looking to the future of mobile advertising, Keister said: “It’s an excellent question and I’m not sure I have all the answers there. But we do believe the pay-per-phone call model on mobile devices is going to be very important.”