It seems that users always have to face problems with each release of iPhone, the early adopters at least. Users are reporting bad screens and a conspiracy theory is also on the rise about iOS4.
Some users have been reporting an error “Your iPhone activation session has expired” when they tried to activate their iPhone 4 via iTunes. The solution is very simple. Restart your iTunes and try, if that doesn’t solve your problem then restart your computer or MAC and that should do the job.
Enjoy your new iPhone 4!