AT&T handsets, starting today, will default to Yahoo!’s oneSearch software in the carrier’s Media Net on-deck portal.

Through oneSearch, customers can access news, financial information, weather, Flickr photos, and other Web content in addition to personal options such as ringtones, wallpaper and games – with Yahoo!’s inline advertising, the companies said.

AT&T’s main rival, Verizon Wireless, has a similar deal with Yahoo!’s main rival, Google.

Such partnerships are expected to become increasingly common as mobile operating systems become more open and as the concept of mobile search itself becomes more of a mainstream activity.

Movies and politics currently are the top mobile searches, a recent study found.