I alluded to this in a post last night, who knew it would be news the next day. Talk about timing.
The 2 million mark listed is around the most accurate we have, of course that is with no official sales figures from HTC. And suffice to say I'm sure HTC was expecting to close the gap between them and Samsung further with this phone. T-Mobile won't have much impact because despite a carrier like Verizon not offering it at all, T-Mobile's been offering it in some areas. It's only now available nationwide so sales should pick up naturally, I just wouldn't expect a major bump. If a bump were to occur though it would be from Verizon since the phone isn't offered at all. I'd say one thing that is at HTC's disadvantage is that a couple of those on Verizon or T-Mobile that lived in an area without the One decided not to wait and bought an S4 and are locked into it. This is going to hurt HTC in the long run as well as the delay that happened earlier this year which will probably hurt them the most.
Another thing that is at HTC's disadvantage, and Samsung's really with slumping sales, is that I believe people are waiting on the iPhone 5S and iOS 7 before they jump to these phones and Android. I wouldn't be surprised to see both phones pick up if the iPhone fails to deliver. This is the only reason I have for why the S4 is slipping like it reportedly is, but then again maybe Samsung's market saturation is playing a bigger role in it then I'm currently calculating. Either way, the iPhone is a big domino in all this.
That said, as a consumer I'd wouldn't worry about it, there's really nothing anyone can do about it anyway. Besides, you have the phone you wanted. But if you're looking at from within HTC's offices you've got to be a little disappointed, simply because this phone is regarded as the best android phone on the market, and in some circles best Android phone ever made, yet it's barely making a dent. The Xperia Z, a phone not even commercially available in the US yet has sold double it in about a month and 10 days time. The One has been on sale since early March for territories outside the US, and late March for North America. I'm not sure if the money calls for it, but they might need a more aggressive marketing scheme.