Smaato says Symbian users in the United States are nearly three times more likely to click on a mobile ad than on an iPhone, according to April metrics from the company’s mobile ad network.

Smaato gave Symbian a score of 339, compared to 125 for the iPhone. The figure is likely to come as a surprise since Symbian has a comparably weak presence in the United States compared to the iPhone.

Europe told a different story, with phones based on Windows Mobile taking a surprise lead with a score of 126, followed by the iPhone at 122. Symbian fell to third place in the European market with a score of 111.

“This data helps to show that even in its home markets, the iPhone, while still strong, is not the top performing OS in terms of CTR – which could well be one of the reasons Apple is looking to try to re-invent mobile advertising to engage its users,” said Smaato in the report.

Symbian dominated on a global basis thanks to the sheer number of phones based on the operating system, which is backed by the world’s largest handset manufacturer, Nokia.

Feature phones’ click-through rates continued to gain on Symbian on a global basis, inching up 9 points since March. Both Symbian and feature phones bucked a global trend toward decreasing interest in mobile ads.