No current generation Windows Mobile 6.5.x phones will be upgradeable to Windows Phone 7, according to Microsoft. This sort of dashes the hopes of some who expected the HTC HD2, at least, to be upgradeable. Sorry, but it ain't happening.

Despite the HD2 meeting many of the criteria laid down in Microsoft’s 'Chassis 1' spec – including a 1GHz Qualcomm processor, high-res capacitive touch display, 5 megapixel camera and 3.5mm headphone jack – the phone will be ruled out for the simple reason that it has five buttons instead of the three mandated for all Windows Phone 7 devices.

That’s the official line from Microsoft, at any rate. Natasha Kwan, General Manager for Microsoft’s Mobile Communications Business in the Asia-Pacific region, told APC that the HD2 "doesn’t qualify because it doesn't have the three buttons."

"Because we have very specific requirements for Windows Phone 7 Series the current phones we have right now will not be upgradable," Kwan explained.

For its part, Microsoft says it will not abandon the current Windows Mobile 6.x platform once Windows Phone 7 arrives. The OS will be rebranded as Windows Phone Classic and retained for budget-minded smartphone buyers as well as business customers with 6.x-based apps.

"We think there are people who will want 6.5, and the 6.x platform has a lot of enterprise and line of business apps," Kwan says.

Microsoft will update Windows Mobile 6.5 to 6.5.3 before the Windows Phone Classic rebadging takes place, and Kwan says this will enhance the experience for 6.5 users.

"A lot of 6.5 applications have been built very much from the old paradigm of the stylus. Those legacy apps will be a lot more compatible on 6.5.3 because we have magnifier technology which lets you use your finger for navigating, even though it has a much bigger surface area."