Not necessarily a sale of its mobile unit, yet, as has been reported before, but InfoSpace (NSDQ: INSP) has sold off its online directory business, including Switchboard.com, to yellow-pages publisher Idearc (NYSE:IAR) for $225 million in cash.

After the close of the deal, expected end of this year, InfoSpace will return the net proceeds from the sale to shareholders as a special dividend. At closing, InfoSpace’s cash position is expected to be in excess of $400 million. Switchboard.com site was acquired by InfoSpace in 2004 for approximately $103 million, and formed the majority of the revenues for its online directory business…For the first half of 2007, this business had revenues of $17.2 million. The business employs approximately 50 people.

Idearc’s owns online directory platform Superpages.com. Just last week it announced a $3.3 million strategic investment in AmericanTowns.com and acquired the URL LocalSearch.com. Superpages.com’s network had 21.3 million unique visitors in August 2007 and InfoSpace Directories and Resources had 7.7 million unique visitors in the same time period, according to Comscore.

More info in release.