my iphone 3g cannot be activated because the activation server is temporarily unavailable. i've been trying it for several times how ca i activate my iphone?

There are 4 possible causes of this error:

• The activation server really IS unavailable. Rare, but it happens. Usually fixed within minutes.
• Your antivirus or firewall (or your router's firewall) is blocking access to the URLgs.apple.com on ports 80 and 443.
• Your phone is jailbroken.
• Your phone isn't jailbroken, but the computer you are connected to during the restore or update was used to hack or jailbreak some other iOS device, and its network database was corrupted in the process.