On an interesting podcast over at Platform Biased, Daniel Smith who's a CX-XBLA Producer at Microsoft, reveals some interesting numbers about those first generation handsets. Out of the three that came out (putting the Dell Venue Pro to the side), the Samsung Focus (see our review) reportedly accounted for about 90% of the sales while the LG Quantum (review) had about 8% and the HTC Surround (review) only garnered a meager 2%.
Smith doesn't mention AT&T directly nor does AnythingbutiPhone (where we grabbed this story from) but obviously that can't be the whole tale. T-Mobile launched the HTC HD7, Sprint followed months later with the HTC Arrive and Verizon even later with the HTC Trophy. T-Mobile and AT&T also both had the Dell Venue Pro, though that was an unofficial as it was never available in stores. Likewise, AT&T eventually picked up the HD7s (review) late in the game.
So there weren't three Windows Phones but rather nine for the first generation and the three mentioned were AT&T specific.
Reported percentage of AT&T 1st Gen Windows Phone sales
Still, it was quite obvious that the Samsung Focus, which is getting a sequel this weekend, was always the big seller on the platform early on and for good reason. It also explains why we'll probably never see an HTC follow-up to the Surround and why LG became gun shy on Windows Phone.