Yahoo! announced today that it is partnering with AT&T to provide mobile ads to AT&T’s 70 million mobile customers. According to Reuters:

A Yahoo executive said in a phone interview the new deal brings its services to up to 70 million AT&T mobile customers. Yahoo will provide Web search on the customer portal for AT&T Mobility customers and deliver ads to AT&T customers who use the Internet on their mobile phones, he said.

“We are actually gaining more subscribers; we are going to gain more search traffic,” said Marco Boerries, executive vice president of Yahoo’s Connected Life division, who oversees the Internet media company’s broadband and mobile phone business.

AT&T’s Mobile Internet portal, MEdiaNet, is currently using Infospace/Motricity for on-portal search, and JumpTap for off-portal search. But it’s not clear if Yahoo! will replace them or just come on top of these existing search services.

Yahoo! proves again that they want to grab the biggest share of the mobile search advertising industry, and they are counting on strong partnerships such as the one with US’ biggest cell phone company to achieve their goal.