For those who want a simple bulletproof interface and OS, there's iOS, if you want a very customizable (and powerful OS) there's Android.
Unless one of them really screws up, Windows has virtually no chance.
And if they want to increase marketshare, they need to heavily subsidize the phone, and the OS, give the OS away for 2 years, and give the carriers a $50 subsidy on each phone sold.
		
		
	 
I'm not so sure iOS' interface is bulletproof. There are still instances where it feels just a tad bit too outdated, even compared to apps in the same ecosystem. Take MobileSafari's interface as a prime example. Google search bar takes up 1/3 of the left side on the address field until you tap on it, so you can't see the whole address at any give time. Plus the color theme is completely out of touch with the rest of the whole OS, and to top it all off, going into Reader mode is like going into a whole different app.
That's just one example. There are many more "inconsistencies" with iOS' interface that I think Apple should fix (urg, try Notification Center!). That same interface has stuck around for... 5 generations of the phone already. Some tweaks are necessary now in order to make it look more modern.
And I'm saying this because I know Apple can get down to it. They did fix the interface of the iPad version of iOS in just 2 iterations of the OS. Somewhat... But it was done anyhow, and there's no excuse to avoiding the same tweaks on the iPhone and iPod Touch.
The same thing can be said about Android, and more. Customization is something I don't think you can find in just about any Android handset. It also depends on whether the user actually knows how to customize the phone. I don't think "set this as the current launcher" is an apparent built-in prompt in Android, and it doesn't appear until someone downloads or installs a new launcher, but if the user doesn't even know what a launcher is... well, you get the idea. At least the Android team is not afraid of trying out new interfaces, and I applaud them for that. Apple can learn a thing or two. They are playing it too safe.
But that's to say, I think MS definitely has a chance in the race, but they are too stubborn with Metro to move on. They are also not trying too hard to increase market presence. I can't recall the last time I saw a good Windows Phone ad that could precisely tell me why I would want a WP7 phone over an iPhone, or an Android phone. I also can't recall the last time I saw a billboard with a WP7 phone superimposed, but I have seen plenty of iPhone and Android.
That's why I said carriers and manufacturers aren't the problem. But it seems someone at MS is too hard-headed to see...