Mobile developers are fuming over a new "a bit evil" Vodafone system that is preventing many mobile businesses from working as intended on Vodafone handsets.

Some fear that network changes recently made by Vodafone in the UK could prevent new and innovative mobile services from reaching the market.

Wireless Ink, a New York-based company operating a service called Winksite that lets anyone develop their own mobile web page, is one company impacted by the change.

Winksite is a service for letting users build mobile web pages from their PC browsers. But when users visit the Winksite page from their mobile phones, they see a different website that lets them view sites developed by other Winksite users, said David Harper, the founder of Winksite.

But since the change at Vodafone, UK mobile users instead see a reformatted version of the PC website.

That's because Vodafone recently implemented technology from Novarra that rewrites PC-targeted websites to display better on mobile phones. But mobile service developers say Vodafone has also started to strip out the user agent string when mobile phones access websites. The standard user agent string tells websites what kind of device and browser a visitor is using. It allows a mobile site publisher to deliver pages optimised for a user's particular phone.

Companies that sell ring tones or graphics also rely on the user agent to determine which content to send to the user that will work on their phone, Harper said.

Companies that are on Vodafone's "white list," which is a group of Vodafone-approved services, were notified of the change and the operator is passing the user agent correctly for those services, developers say. Some developers complain that it's difficult to find out how to get on the white list, it can take several months to get added and that Vodafone requires white list companies to make certain changes to the way the included sites operate.

If all operators had a similar process, service providers like Harper would have to get on the approved list for every operator around the world. That's comparable to asking any web service to be approved by every ISP in the world in order to operate.

"If this were to spread from carrier to carrier it would be horrible," Harper said. About 10 percent of his traffic comes from the UK. He worries that small mobile companies that are solely targeting the UK will be even harder hit. Winksite users include individuals as well as companies like Warner Music which uses the service to build web sites for musicians.

It's unclear if Vodafone removed the user agent capability for "diabolical" reasons, such as to maintain firm control over the content that users can access, or if it was a legitimate mistake, Harper said. On a developers forum hosted by Vodafone, one poster who appears to work for Vodafone has defended the move and said that most customer feedback has been positive. He also said that many other European operators are in the process of implementing similar technologies. Vodafone was not available for comment.

Mobile services developer Lucca Passani, who has blogged extensively about the problem, worries that if Vodafone hasn't received user complaints, there's a simple reason. "The great majority of consumers won't realise that they have been deprived of a service and will not complain," he wrote.

Harper and other developers don't take issue with the technology that can translate sites designed for PCs but they say that Vodafone doesn't need to block the user agent string for mobile sites in order to support that capability.

"The bottom line is, they've done something a bit evil and they need to fix it," Harper said.