The Nokia Lumia 900 is finally ready for Windows Phone 7.5. Nokia's flagship device will not be getting the upgrade to Windows Phone 8 this fall, but AT&T has promised it will be getting the watered down version, firmware 7.8, after 7.5. AT&T would only say the update was being readied "in the coming weeks," which could be a large range. Additionally, the carrier is adding a usage ...