OK, let's be super-conservative and assume that every bit of Android growth from T-Mobile's launch onwards was only from Verizon (a very dodgy assumption, but bear with me).
Let's assume T-Mobile had a similar launch with Lumia 920.
That would make the T-Mobile Lumia 920 2.5% of the smartphone market in the USA for 2/3 of the last quarter of 2012, or 1.65 million total T-Mobile Nokia Lumia 920s sold.
And that's in the WORST case, rosiest pro-Verizon forecast.
That means that in Q4, T-Mobile would sell twice as many 920s than Nokia has sold all Windows Phones combined in the USA in the prior year.
Contrast that to the Lumia 900 launch on AT&T, another carrier exclusive, which sold a mere 300,000 units and then immediately fell off the sales chart.
Which makes more sense? (Especially considering that Verizon isn't planning a "Droid-style" launch campaign around the Lumia 920 in Q4 of this year, and AT&T is giving the 920 no more support than it gave the 900 earlier)
Nokia is suffering from the classic Innovator's Dilemma. They're going to market with assumptions that are obsolete (carrier exclusives are good) in a market that has been entirely disrupted. As a result, they will fail as surely with the AT&T 920 as they did with the AT&T 900, for exactly the same reasons.