It will not be called Windows Phone 7 and previously added Series at the end has been removed by Microsoft as commented on WP7 official Twitter account.
Tis the season for Series finales. We’ve got one too – dropping the ‘Series’ and keeping the ‘Windows Phone 7.’ Done.
It is a smart move on Microsoft’s part as many were confused about the future offering in the same category. Keeping “series” at the end would have meant that there are more OS updates or upgrades for something else [Xbox??] coming in pipeline too.
It now sounds better, it looks better [at least in terms of when you see it written] and it will definitely give a good abbreviation to the OS. Kudos to the genius coming up with the idea to ditch it and make it smaller and sexier.