AT&T Entertainment Pack - Home
AT&T is offering a few freebies for Windows Phone users: a free download of the Xbox Live Enabled ilomilo game (kinda reminds me of Portal a bit) as well as a month Zune Pass subscription (believe that is 2 weeks longer than the default Zune offer). There is also a free month of AT&T U-Verse Mobile (but I think you can get that just by launching that app.).
You can also get the game by TEXTing WP7 to 123 from your new AT&T Windows Phone and they'll send you a link in a free text message.