A new metrics report from ad optimization company Smaato highlights the difference in click-through rates seen on different phone operating systems.

The winner? Symbian, by a wide margin.

Smaato runs an ad optimization service, and delivers ads from a wide variety of ad networks to a wide variety of publisher sites. In December 2009 almost 3 billion ad requests were served through the Smaato Network.

This month Smaato has released some interesting metrics based on these 3 billion ads, looking at CTR on the various mobile handset families, as well as the “fill rate” from different ad networks in the US and globally.

For the Click-Through metrics, Smaato first calculated an average click-through rate across all handsets, then assigned CTR an index of 100, and finally looked at the variations compared to this average as seen on the most popular handsets.

Symbian handsets out performed all others with a score of 161, with the iPhone/iPod Touch platform coming in second at a level of 119.

Coming in just under the average was the “Feature Phone” category, but surprisingly Android was significantly below average at a 65 index level.

Also noteworthy are the very low click-through rates seen by RIM Blackberry and Palm devices. These were indexed at 26 and 28 respectively, meaning that they yield less than 1/5 the clicks as the leader. These may be due to the high percentage of business users on the RIM and Palm platforms.

Of course these days mobile advertising and marketing can include many levels of interactivity beyond simple click-through, but banner ads are still widely used and it is still very interesting to see a variation in CTR of this magnitude.

For the full Smaato Metrics report, visit the Smaato website.