Now that Google's $12.5 billion purchase of Motorola Mobility is a done deal, the internet giant has been dragged into the high-stakes smartphone ad battle.

Leading that charge will be Gary Briggs, former Google VP-consumer marketing, who is replacing Bill Ogle as Motorola Mobility's chief marketer. Mr. Briggs' appointment was announced along with a major leadership overhaul at the company. After the acquisition cleared the last regulatory hurdle early this week, former Motorola Mobility CEO Sanjay Jha stepped down as Dennis Woodside, who previously served as president of Google's Americas region, took the helm.

On the marketing front, Motorola and now Google are up against stiff competition. Motorola, which operated at a loss last quarter, is selling fewer mobile devices in the face of soaring Apple and Samsung popularity. The stakes are also increasingly higher in handset advertising, especially in the U.S. Samsung, the manufacturer that 's stormed the smartphone market with devices running Google's Android mobile software, was the first smartphone maker to run a Super Bowl ad for its Galaxy Note this year.

What's more, Motorola has less in its marketing artillery to stave off those big ad spenders. As for Google, the company has only just begun to ramp up its own ad efforts, turning to more traditional media like TV. Before Google, Mr. Briggs held marketing posts at eBay, PayPal, IBM and PepsiCo, according to his LinkedIn profile.

Motorola spent $43.9 million in U.S. measured media last year, according to Kantar. Globally, Motorola reported $560 million in advertising expenses for 2011, up from $393 million in 2010.

Both Apple and Samsung were among the top 100 global ad spenders in 2010. Motorola was not.