n Microsoft Corp. has started placing advertisements on the U.S. version of MSN Mobile, a Web portal for cellphone browsers that connects users with Hotmail, instant messaging, search, news and other content.

Microsoft already serves up mobile ads in Japan and some European markets. Competitor Yahoo Inc. began selling cellphone ads phones in the U.S. in late 2006 and expanded overseas in February.

Microsoft said the cellphone ad service is a mix of its own efforts and those by two companies it acquired this year ر online advertising company aQuantive Inc., to the tune of $6 billion, and mobile ad group ScreenTonic SA, which it bought for an undisclosed amount.

Viacom Inc.صs Paramount Pictures, Ford Motor Co.صs Jaguar car brand and Bank of America Corp. will be among the first to peddle their brands to U.S. mobile customers, starting Monday.