InfoSpace today said it is selling its mobile services unit to Motricity for $135 million in cash, making a leaner Web services company focusing on online search.

Motricity officials said the two companies’ mobile platforms compliment each other well--InfoSpace’s mCore platform and Motricity’s Fuel platform offering many of the same storefront, messaging, portal and managed Web services. InfoSpace, however, brings to Motricity’s portfolio a powerful mobile search function, originating from the company’s core Web search technology. The combined platforms will also give Motricity a broader customer base. Motricity officials said the acquisition will increase its penetration in North America from 7 to 10 of the top 12 carriers, and its portal services will power the start screens of 5 of the top 6 operators.

InfoSpace last month announced the sale of Switchboard.com, its mobile Web services directory, to Idearc for $225 million. The sale announced today would further slim down the company so it can concentrate on its sole remaining business. “With these transactions, InfoSpace will be solely focused on online search,” Jim Voelker, chairman and CEO of InfoSpace, said in a statement. “Our search business is highly scalable and continues to generate strong cash flow.”

InfoSpace builds private-label search portals such as Dogpile.com that aggregate the results of other search engines. The Motricity deal is expected to be completed in three months and will result in the mobile services unit going private under Motricity’s umbrella. Current Motricity CEO Ryan Wuerch will remain in his current role, while InfoSpace executive vice president of mobile services Steve Elfman will become Motricity’s president and chief operating officer.