If WP8 would like to take off in the US, it has to move off AT&T
Lets look at some numbers shall we?
For a few months, the Lumia 900 was the second highest selling smartphone on AT&T, comprising of a quarter of all non-iPhones.
Yet, it only sold about 300000 (which actually makes my wonder sometimes, are non-iPhone exclusives on AT&T even profitable? As in devices like the Atrix familly, One X, Focus familly, etc.)
For Windows Phone to stand a good chance, it has to move off the iPhone stronghold AT&T. WP7 did pretty well to be honest, after all, the Lumia 900 managed to outsold popular models like the Atrix 2, One X, Focus S, etc.
Consider this, if windows Phone manages to take 25% of all non-iPhones on Verizon, that would be BIG. Hopefully WP8 can replicate the success it had on AT&T on Verizon and T-Mobile (unfortunatly, sprint doesn't want to support WP8). 25% of all non-iPhones on AT&T, Verizon, and T-mobile would mean that WP8 can easily surpass Blackberry, becoming a strong 3rd place player, with hopefully 20%.