During their announcement of Windows Phone 7 Series at Mobile World Congress 2010, Microsoft also announced that the Big Blue would be the “preferred partner” of Windows Phone 7 in the United States of America reports an article over on pcworld.

Obviously all the issues and flack AT&T has seen from its customers and the attention of the media therein, and of course the network coverage battle with Big Red Verizon Wireless hasn’t stopped Microsoft from having AT&T as the ‘chosen one’.

AT&T must have something as Apple chose to remain with AT&T with the iPad and it is expected AT&T will retain exclusivity over the iPhone, and Apple execs have voiced their opinions on just how good AT&T is.

And now Microsoft joins in the AT&T backslapping by giving them the newly branded Windows Phone 7 Series operating system, and although no doubt all four major US carriers will gain Windows Phone 7 Series, Microsoft CEO Steve Bullmer singled out the Big Blue as Microsoft’s “Preferred Partner,” which could mean AT&T will get exclusivity over the best handsets sporting Windows Phone 7 Series pr preferential treatment when Windows Phone 7 becomes available.