Read into that slide what you will, but it sure looks to us like Microsoft is calling 'Mango' Windows Phone 7.5, at least internally.

However, when we asked Andrew Clinick from Microsoft, he said that it was a "mistake" calling it 7.5 in that slide and that they haven't decided on what they are calling it yet. So backtrack/covering or legit position? We have no idea, but figured it was worth mentioning, at the very least.