The installed base of Windows Phones have always been a closely guarded secret by Microsoft.
After Apple announced 80 million Mac computers in use multiple Microsoft-friendly journalists, such as Ed Bott above, however noted this is the same installed base as Windows Phones.
The number seems a bit high however, and I would place it closer to 50-60 million, based on the last two years of sales of Windows Phones sales according to the IDC, but maybe Ed is quoting a statement made by Microsoft at some point.
Apple also announced more than 500 million iPhones sold, but of course not all of those iPhone 3GS are still in use. With the Windows Phone installed base close to 20% of the iPhone base, should our platform be getting more attention?