Windows Mobile has edged ahead of Apple in mobile advertising performance, according to the Smaato Worldwide Index.

Smaato, a mobile ad optimiser and advertising agency, has released a global mobile advertising metrics report, which analyses ad network fill rates and click-through rates (CTR) segmented by handset operating system, geography and response times, covering the ad fill rates of the global top 10 advertising networks.

The Index revealed that Symbian continues to lead the pack, with Android a distant second.

The biggest surprise is the lead Windows Mobile has over Apple – the iPhone and iPod Touch show a declining CTR, coming in with a rate of 89.

This is the first time Apple devices have dipped below the average Index of 100, and the first time that Windows Mobile has edged ahead of its rival. In December 2009 the iPhone posted a CTR Index of 119, sliding to 104 in January 2010.

BlackBerry comes in at 51, up from 30 in December 2009, while Symbian – still the dominant operating system – has dropped slightly. It comes in at 147, compared with 173 in December 2009.

The index is based on data collected from 35 mobile ad networks and over four billion ad requests served in the Smaato network of more than 3,000 registered mobile publishers in February 2010.