Microsoft on Sunday night unveiled a deal with Sony Ericsson, which will see the Swedish-Japanese mobile handset maker use Microsoft’s Windows Mobile operating system in a new flagship handset to be launched later this year.

The deal is a coup for Microsoft, which is now working with four of the world’s top five handset manufacturers. It already has deals with Samsung, LG, and Motorola. Only Nokia has resisted working with Microsoft, and this is unlikely to change, given the company is backing rival mobile phone operating software from Symbian.