When it comes to mobile search and paid-search clicks the iPhone still drives most of the volume. However, ad aggregator and optimizer Smaato says that iPhone and iPod Touch display click-through rates (CTRs) have declined and that Windows Mobile has now pulled ahead. Symbian is the king. 

The data in the chart below represent concentrations in the US and Asian markets. Smaato is looking at "performance" in 35 mobile ad networks covering "more than 3000 registered mobile publishers in February 2010."

An index score of 100 is the average CTR. So in the chart above, Symbian, Android, "featured phones" over-index -- meaning their users click more -- and those below 100 are under-indexing; their users click less. 

Smaato comments on the decline in the iPhone/iPod Touch CTRs:

One of the big surprises is the continuing decline of CTR Index from iPhone and iPodTouch with a rate of 89; it’s the first time Apple devices have dipped below the average Index of 100. In December 2009 the iPhone posted a CTR Index of 119, sliding to 104 in January 2010.

There will be a good deal of unreflective discussion of these findings. It's important to point out as a fundamental matter that clicks as a display metric are inadequate and fail to capture the real influence of dispaly advertising online. There is now a substantial body of evidence that display ads influence purchase behavior despite a lack of clicks. 

So while these data are interesting, they don't necessarily correlate with actual purchase outcomes or brand influence on consumers from mobile display ads.