Marchex, an online advertising company, plans to announce today that it is entering the mobile market via its subsidiary VoiceStar, which it acquired for about $20 million last August. As part of the announcement, it said the subsidiary will be providing call-based advertising services, or “pay-per-call” information to three leading mobile advertising providers: AdMob, Ringleader Digital and 4INFO. VoiceStar can identify the ad that generated the phone call, and report the length of the call and when it and where it took place. The calls can also be recorded. The advertising partners, including AdMob, will use the service to charge advertisers for the phone calls they are responsible for delivering to them.

Another company, Ingenio, is in the pay-per-call business. It was acquired by AT&T (NYSE: T), which planned to it integrate into its yellowpages.com business. At the time of the merger’s close in December, we reported that Ingenio was handling calls for AOL,, Miva and even Marchex. Marchex acquired VoiceStar four months earlier in August.

• AT&T Completes Purchase Of Ingenio; Company To Be Joined With Yellowpages.com