Google, Inc. (NASDAQ: GOOG) ventured further into mobile advertising this past week with the introduction of display ads geared for mobile phones. From the smallest cellphone screen resolution to the iPhone, Google wants to ensure that it will be able to display ads on all those billions of tiny screens in the very near future. This should come as no surprise, as CEO Eric Schmidt seems to always promote Google's mobile efforts every single chance he gets. It's no surprise -- there are way more mobile users in the world than there are PC users.

Can Google become as successful on the mobile screen as it has been on the PC screen? That's a tough one to chew on, but the extremely limited real estate of a cellphone screen may make that effort quite difficult. Google just can't line up paid ads down the side of a cellphone screen like it can on that laptop screen or that 21" LCD monitor on the desk at home or in the office.

The iPhone changed the game a bit last year, giving customers a very large screen -- both physically and in resolution -- to play with. However, the number of iPhones pale in comparison with total cellphones with a smaller color screen. Google's Android cellphone operating system, which has a huge partnership following, may be able to increase available inventory on the mobile screen for Google's ads. In fact, that was probably a top priority. However, it will be quite a while before customers have that at their fingertips. Google's mobile ad efforts, until then, will be highly complementary to its regular advertising business on the PC screen, but nothing more.