I talked to Apple today about the same issue. Apparently the 'activation server' is presently being worked on for maintenance or for other reasons. I was told this at about 2:30 PM. The woman told me to wait and try to reactivate every 30 minutes. However, it still does not work for me currently. I'm guessing that our best bet is to wait till morning and give it another try.
Have you guys been able to activate your iphone yet? I bought an iphone 4s from eBay and it worked fine, but the previous user had left some data on it, so last night I used the "erased all content and settings" to restore it to factory setting so I can start fresh and restore my backup. But now I'm stuck at the activation screen (I get the same "the activation server is temporarily unavailable") and can't get it to activate, even if I use my old deactivated AT&T sim card (I'm on straighttalk now).
I might try activating it with an active AT&T sim card from my fiancee's phone when she gets home, so I'll let you know how that works outs.
If it's true that the server is down; anyone know when it will be back up again? Thanks in advance.
iPhone 4s iOS 5.1.1 (9B206)
Carrier AT&T 12.0
Modem Firmware 2.0.12
The two most obvious possibilities are that the phone was hacked or jailbroken by the previous owner, and the modem firmware does not match the iOS version, or that you are trying to activate it using a computer that had previously been used to hack or jailbreak some iOS device in the past.
In order to activate iTunes must be able to reach the activation server at gs.apple.com. So a 3rd possibility is that your antivirus or firewall is blocking access to that site.
You should check the hosts file on your computer. If there are any records containing gs.apple.com you should delete them and reboot your computer. Locations: