Some Nokia Lumia 900 handsets having trouble connecting to data networkshttp://www.engadget.com/2012/04/09/nokia-lumia-900-data-connection-issue/
By Michael Gorman posted Apr 9th 2012 at 3:15PM
Nokia's latest Lumia, the 900, has been rightfully lauded for its low price and lovely polycarbonate shell, but apparently, all is not well with the new handset. According to forum posts on Nokia Support Discussions and elsewhere, some 900s aren't able to connect to any of AT&T's data networks.
The affected phones get data reception initially, but once the connection is severed by turning the phone off or placing it in airplane mode, it fails to reconnect. Some have successfully solved the problem by removing the SIM, performing a master reset, shutting the phone off, reinserting the SIM and turning it back on.
However, it looks like that solution isn't working for everyone. It seems the problem has appeared in a limited number of Lumias, so we've asked AT&T about the issue and are awaiting an official response on the matter while it investigates.
Nokia Support Discussions, WPCentral forums