In addition to the FCC documents, reports from BoyGeniusReport and MobileTechWorld indicate AT&T plans to introduce a LTE variant of the Lumia 800 with a larger display and LTE support. It appears to be designated the Lumia 900 by Nokia, and probably the Nokia Ace by AT&T.
SlashGear is now reporting there is a $100 million promotional campaign planned to promote the Nokia Ace when it launches in late March. Likely there will be more details on the launch given at Nokia's CES presentation next week.
On one hand, the partnership with Nokia on Windows Phone has always made a certain amount of sense from Microsoft's point of view. Prior to the iPhone, Nokia was the biggest name in smartphones worldwide.
But in the US, which admittedly is only one of many important markets, Nokia has never been known for their smartphones. At least in the beginning, Nokia Windows Phones will likely attract US buyers more on the strength of Microsoft's name than Nokia's.
Right now both companies have a long road ahead of them to establish a brand identity among US consumers. Carrier promotions are an important component of that. In a country where carriers, rather than handset vendors, sell phones, it's the only path to success.