“A little while after the Lumia 900 went on sale, we discovered a software issue that can sometimes lead to lost data connectivity. This issue is purely in the phone’s software, and isn’t related to the phone hardware or the network itself.
We apologize for any inconvenience this may have caused, and as a gesture of goodwill, we are offering a $100 AT&T bill credit to everyone who has already purchased a Nokia Lumia 900 or who will purchase one before April 21st. “
Connect your phone to your computer, using the USB cable that came with your phone.
If the Zune software or Windows Phone 7 Connector for Mac doesn’t start automatically when you connect your phone, start it manually.
In the Zune software, click Update Now (in Windows Phone 7 Connector for Mac, click Install Updates). Make sure you keep your phone connected to your computer until you see a notification that the update is complete.
How to prepare for an firmware update?
Verify that your phone is set to the correct date and time. That helps us determine which updates you need.
If your battery level is low, connect your phone to a charger before starting the update.
Make some room on your phone for the update. If necessary, remove a few unwanted applications or other large items. To see how much free space you have on your phone, select Start, then flick left to the Applications list, choose Settings > About and look at the number to the right of Available storage.
Free up space on your computer as you will need some room to download the software update, to save a backup of your existing phone software and settings and possibly to synchronise media files from your phone to your computer.
Note:- When you install an update, all of your settings, applications and media files are preserved.