Recent FCC documentation shows that a new Windows Phone device made by Chinese manufacturer ZTE has passed certification. There are not many details on the N859, as it is called, other than that it is CDMA-only and will be running Windows Phone 7.5 (Mango). One N859 has popped up on Occasional Gamer's gaming stats page, so we know there is at least one out there being tested in the wild.
It's a little odd that ZTE would be looking to release a WP7.5 device so close to the launch of Windows Phone 8 (Apollo), as many consumers will likely just hold off on buying a new phone so they can get the latest and greatest. However, ZTE tends to target emerging markets and cost-conscious consumers, so perhaps they are betting on demand for a more economical device with fewer bells and whistles.