activation required

Activation requires your cellular carrier. Here's how to contact them:

Contact a mobile carrier

I have this same problem, I am not currently in the U.S, so I'm guessing I can not use it until I return? I was thinking it may have been a no service problem.

Are you running a Beta version of iOS7?

The Beta version has expired, and must be updated to the Public Release version of iOS7.

You will need to update by connecting to a computer running iTunes.