Your iPhone could not be activated because the activation server is temporarily unavailable My iPhone 5 that has been running iOS 7 since beta 1 suddenly wants to be activated.  When locked, it shows me my wallpaper. After sliding to unlock, it asks for my passcode. When I enter it, it takes me straight to the 'Activate iPhone' page - like it wants to be set up.

The text on the page:


  This iPhone is currently linked to an Apple ID (e**@icloud.com). Sign in with the Apple ID that was used to set up this iPhone.


After I input the correct credentials and press Next in the top right corner, the title of the page changes to 'Activating...', then changes back to how it was before.

About 15 seconds later, it transitions to a 'Could not activate iPhone' page:


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


Has anyone encountered this problem before? Is there a solution to it?
The two major causes of this are:


Network related - change the network used to connect
iOS related - something is amiss with the code signing / provisioning


The most likely cause of software is a beta. Apple disables the iOS betas soon after the release happens. If you never manually installed the official release, this can happen. If not, consider backing up your device after checking a couple networks and reinstalling.

If you need to get a beta off, do the following to fix it:


Hold the Power and Home buttons until the phone reboots and you see the Apple logo.
Release the Power button but keep holding the Home button.
Release the Home button when you see the iTunes logo and the connector below it.


Do this while connected to iTunes. Click Restore. Hopefully you have a recent back-up.

Note: It is a large update and will take a while. Apple servers are currently getting slammed.