AdMob has released their December Mobile Metrics report, and the data shows that smartphones continue to grow in the market, representing 33% of AdMob’s ad requests, up from 22% in May.

The market share of the key players is rapidly evolving as well, with new entrants gaining rapidly.

Some of the more interesting points from the study include:

• Symbian is still the #1 smartphone OS worldwide with 41% share. iPhone is second with 32%. However Symbian retains more than 90% share in Africa and Asia, while the iPhone is strong in Europe and Latin America.
• The RIM OS and Windows Mobile lag Symbian and the iPhone OS with 10% and 9% share, respectively. A majority of RIM and Windows Mobile requests come from North America.
• The Palm OS has 4% worldwide share with more than 95% of its requests generated in North America.
• Only 2 full months after launch, Android has captured 2% OS share and is slightly ahead of Symbian in the US.

The report also includes more detailed data about the US, UK, Indonesia, India, Philippines, and South Africa markets.