Sony Ericsson's yet-to-launch Xperia X1 is facing stiff competition from the BlackBerry and iPhone.

Sony Ericsson has denied rumours that its first mobile phone powered by Microsoft's operating system would miss the key Christmas sales period.

Sony Ericsson introduced the Xperia X1 model in February, saying it would start to sell the phone in the second half of 2008 in selected markets.

"There is absolutely no delay. The product is on track," a Sony Ericsson spokeswoman said following news reports that the project had stalled.

Phone makers usually unveil new models months before they reach the shops, but introducing new phones more than six months ahead of sales is relatively uncommon.

With Sony Ericsson joining the list of Windows users, all top handset makers apart from Nokia will offer Windows Mobile phones, which, despite years of investment, still command only about 10% of the smartphone market.

Sony Erickson reportedly missed its 20 million phone sales target in the US for the year to June 2008, with stiff competition from other platforms, especially RIM's BlackBerry and Apple's iPhone.