Sony Ericsson is to unveil a Windows Mobile handset at this week's Mobile World Congress (MWC) in Barcelona, formerly the 3GSM World Congress. The move means that four of the top five handset makers are now licensees of Microsoft's phone platform.

The new handset, codenamed Venus and released as Xperia X1, will be on show at MWC but not available until later in 2008. Microsoft said that Sony Ericsson is looking to build a broader product range and recognises that Windows Mobile is a viable proposition.

"We're tremendously excited that we've got four of the top vendors. The world was stunned when Palm announced its Windows Mobile Treo, and I think this will raise a few eyebrows too," said Derek Snyder, group product manager of Microsoft's Mobile Communications business.

Details of the handset are so far sketchy, but it will run "an updated version of Windows Mobile 6.0", Snyder said, and is likely to feature customisations specific to Sony Ericsson.

The development is unlikely to see a shift away from Sony Ericsson's Symbian-based smartphone range. Instead, the intention may be to boost its market share in the US market and in corporations that have a Windows-only strategy, a move that proved successful for Palm.