Stuck in Setup-Loop after Update to iOS 5.1

i upgraded an factor unlocked and unmodified iPhone 4S running iOS 5.0.1 to 5.1 via iTunes last night.

after the update was completed i am not able to enter my homescreen - i alsways get the setup selection for networks followed by the screen saying that setup is finished. after hitting okay the homescreeen appears for a second, followed by a black screen with animated apple logo. next i'm back at the screen with the network selection.

i tried a restore - no solution. i swapped the iphone at the apple store and got a new one wit iOS 5.0.1 and restored it from an (2 weeks old) backup. then i applied the 5.1 update via WiFi (not via itunes). Same result.

As a matter of fact i have no access anymore to my data - though i backed it up by doing iTunes backups.