Yesterday AT&T dropped their big and much-anticipated news on the mobile market: the Windows-Phone-powered Nokia Lumia 900, an upgraded, Americanized version of the Lumia 800, which has been receiving stellar reviews in Europe.

The new flagship Nokia AT&T Windows Phone could cause a huge splash in the mobile consumer market -- and from there, of course, to developers, whose biggest problem with Windows Phone 7 to this point has been its relatively small market-share. The Lumia 900 may answer the mobile developer's 'why develop for WP7' query with the simple answer: 'plenty of people are using it'.

But AT&T enticed developers with another bunch of announcements, not specific to WP7:

• HTML5 app store: competition for the Apple and Android (and Windows Phone) stores, to be sure, but without the threat of buy-in. Mobile developers are moving more and more to HTML5 (Adobe knows what it's doing), and AT&T wants them to sell their products through an AT&T store.
• API platform: AT&T may have learned from Amazon that the platform is, maybe, where the money will be. AT&T announced several new APIs designed to make developing for mobile easier, including:
• 'add that to my bill' technology, removing in a single stroke all developers' worries about payment, and monetization in general. Everyone pays their AT&T bill, and everyone trusts AT&T; so why not get your money through your users' AT&T bill? Should make developers extra-happy with AT&T -- especially if they're already developing in HTML5.
• AT&T Cloud Architect: like the name says, a storage and IaaS platform with developers' interests first -- especially small developers, if I interpret the announcement language correctly.
• AT&T U-verse APIs: giving developers access to receivers running AT&T U-verse software.
• Application Resource Optimizer: presumably designed to help developers optimize their apps for AT&T phones, data plans, and network use overall. 

For more details, check out the official press release, or a live blog transcript of AT&T's CES keynote (if you enjoy that sort of tension). This may prove to be a crucial moment for mobile development, as awesome new Nokia phones arrive in North America, and AT&T throws a bunch of its weight behind Windows Phone -- and also HTML5 (and cloud, and living-room technology..).