CBS Corp. plans to announce today a partnership with four mobile-advertising companies to sell ads on mobile devices for its entertainment, news and sports programming. Marketers will be able to buy text and banner ads for mobile Web sites as well as video commercials for mobile devices as part of CBS Mobile's partnership with AdMob, Millennial Media, Rhythm NewMedia and Third Screen Media. The deal is an effort by CBS to find new ad-revenue streams. The pact comes as media companies are offering more programming -- from weather and sports to news and prime-time shows -- through mobile devices. General Electric Co.'s NBC announced yesterday a deal with Verizon Wireless that makes short videos from nine channels available to subscribers of its V Cast service.