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It sounds like all of a sudden you got a message saying you needed to activate your phone, but for some reason the activation is not finishing as expected.
I was researching what may be causing the issue, and found this article named iPhone: Troubleshooting activation issues found here http://support.apple.com/kb/ts3424.
- Restart the iPhone.
- Try another means of reaching the activation server and attempt to activate.
- Try connecting to a known-good Wi-Fi network if you're unable to activate using a cellular data connection.
- Try connecting to iTunes if you're unable to activate using Wi-Fi.
- Restore the iPhone.
If you receive an alert message when you attempt to activate your iPhone, try to place the iPhone in recovery mode and perform a restore. If you're still unable to complete the setup assistant due to an activation error, contact Apple for assistance.