Google's drive to own the mobile space took a significant turn today, with the search giant announcing that it has expanded the ad volume for its mobile network.

The expansion means all sites accessible via a mobile web browser can participate in the Google's wireless version of AdSense.

According to an Associated Press report, the bulk of Google's $15 billion ad revenue came from online search monetized via AdSense. However, as mobile continues to grow, Google, Yahoo! and Microsoft have all shifted their efforts toward dominating the space.

One mobile rumor that Google seems unwilling or unable to kill is the possibility that the company is working on its own phone as a means to guarantee effective ad serving. Unlike online. where companies such as Google have free reign, mobile is largely dominated by a handful of carriers. That dynamic may be at the heart of Google's GPhone push, which many see as a way for the company to establish a position in the looming mobile ad war.