I updated the iPhone and I can not activate.

I selected the Country, the language, I join the Wi-FI then it try to activate the iPhone but it can't activate. After trying to activate it it says:

Your iPhone couldn't be activated because the activation server is temporarily unavailable. Try connecting your iPhone to iTunes to activate or try again in. Couple of minutes. If this problem persists , contact Apple Support at apple.com/support.

What can I do to activate an be able to use the iPhone?