Alan Mendelevich, who runs Adduplex, which is an ad network on a large number of Windows Phone apps, has just tweeted some interesting findings from a look at his logs.
Apparently he discovered a number of Nokia Windows Phones in the wild.
The list includes the Nokia RM-914 (Lumia 520), so presumably a very cheap low end Lumia, the RM-885 (Lumia 720), a presumed mid-range Lumia, and two other unidentified handsets, the RM-887(?) and RM-860(?) on Verizon.