Clash of Titans: Apple vs. Google

No question, placing ads or branded apps on mobile phones promises to be the Next Big Thing. The problem? People have been saying that for the last three years. Or, has it been five. For mobile marketers, the hurdles are still everywhere. First, there's market penetration. Even though it might look like everybody and his uncle has a smartphone, the truth is that less than a third of Americans (30.6 percent) are mobile Web users, according to eMarketer. So while brands like the idea of wireless marketing -- nearly 65 percent said they plan to invest in mobile apps this year, also per eMarketer -- they have reasons to be wary, too.