Local online media and ad firm Marchex (NASDAQ: MCHX) is buying pay-per-call ad tech firm VoiceStar for $20 million, plus $8 million in additional investments through 2008, reports ClickZ. Also, Marchex has hired Bill Day, the founder of About.com and later CEO of WhenU, to lead its consumer-facing media business as chief media officer.

Marchex distributes ads to 100K of its own local and vertical Websites, as well as to over 100 search and vertical network partners…pay-per-call will now be added to the arsenal with this acquisition. More details in its Q2 earnings release.

AP: Marchex, which received about 31 million unique visitors to its Web sites in June, said it may be the primary driver of revenues to Yahoo’s sites by the end of 2009.