Updated with corrected information about AT&T's participation in next Monday's Microsoft Windows Phone 7 launch.NEW YORK, ( TheStreet) -- AT&T ( T) is not too jammed after all to make Microsoft's ( MSFT) Windows Phone 7 debut party, as originally expected. According to a press invite, AT&T mobility chief Ralph De La Vega is scheduled to take stage in New York with Microsoft CEO Steve Ballmer at 9:30 ET Oct. 11 to kick off a full day surrounding Microsoft's Windows 7 show. AT&T is expected to unveil as many as three Windows 7 phones from HTC, Samsung and LG. Later at the same event Deutsche Telekom's ( DT) T-Mobile will be showing its own Windows 7 devices. Having the two telco partners onboard for the launch of Microsoft's hotly-anticipated operating system helps solidify the software giant's bid to reenter the mobile market after a disappointing turn with Windows Mobile 7 and the failed Kin devices. The big mobile push by Microsoft is aimed at stealing some of the spotlight -- and, of course, the business -- from rivals like Apple's ( AAPL)iPhone and Google's ( GOOG)Android devices. Given the importance of the mobile market and how far Microsoft has fallen out of the game, the Windows 7 debut will probably not spare any expenses as the company tries to make a big splash. --Written by Scott Moritz in New York. >To follow the writer on Twitter, go to http://twitter.com/TheStreet_Tech. >To submit a news tip, send an email to: firstname.lastname@example.org.