Most ZTE phones i've seen have been on pre-pay phones. If they make a prepaid windows phone, it will be the first and hopefully be popular. Windows phones only make up aboust 2% of smartphones (I'm a proud owner of a windows phone) but maybe a prepaid will jump it up to 3%.
I'm a WP7 owner, too. It would be nice to see the it jump up past 2% this year. Honestly, I believe it will, with the Nokia selling so well and Samsung's Focus 2 may help. However, it will not be until WP8 that the market will show any major increases, in my opinion.