Greg Sullivan, senior product manager for Windows Phone at Microsoft, has told Pocket-lint that the current line-up of Windows Phone devices won't be getting the update to Windows Phone 8 later in the year because it doesn't make sense to commit the manpower to making it happen.

"Support for dual-core multi-processors, new screen resolutions, NFC, removable SD card - this awesome Lumia 900 has none of those features, so doing the work to bring those features to this phone doesn't make sense," he explained to us on a trip to London on the way back from TechEd in Europe.

"Instead, what we focused on was making Windows Phone 8 fully exploit the latest generation of hardware, taking the most obvious user changes we are making and bringing that to existing devices."

Rather than NFC or faster processor support for a device that doesn't have it, Windows Phone 7.5 users will be getting a new start screen - among other things - that allows them to get more information at a glance than previously.

Shown at the company's Sneak Peek event in San Francisco last month, the new feature will be coming to Windows Phone users around the same time, if not slightly after the Windows Phone 8 roll out begins.

It's clear though, from talking to Sullivan, that much of the final design is yet to be locked down.

In a quick demo of a Nokia Lumia 900 running an early build of Windows Phone 7.5, we noticed that double-digit notifications on the smaller tiles don't fit. The clock - now rather unsightly - overlays the Live Tiles, and the arrow to move to the app page is now gone (although the app page is still present).

The response from Sullivan?

"It's not clear that the arrow on the start screen may stay gone. We may figure out how to bring it back. It's still early days."

We are sure it will be fixed. Sullivan and Microsoft seem very proud of the Metro design.

"If you type in your Live ID, your Facebook and LinkedIn credentials, right away that phone is more obviously yours than any other platform," Sullivan said.

"It automatically personalises itself. With the new start screen you can take that to another level. The phone really reflects you.

"We've taken this core principle around the design approach around Metro and made Windows Phone about your content. We don't have faux 3D, or pretend highlights. The user interface is trying to get out of the way. We are really tweaking it around personalisation and customisation."

Windows Phone 8 is expected to be launched on a new bevy of smartphones available later in the year.