Whenever I try to create an account on the simulator or device, I get a message "game center account services are currently unavailable. Please try again later."
Furthermore, I have never been able to sign in to the game center app on the simulator.
Interestingly, if I reset my device with iTunes, I can then log in to the Game Center app with my regular apple id. But whenever if I log out, then try to create a sandbox account for an app I am developing, it always fails as described above.