Q: i cannot activate iphone 4 (message is unknown error) ?

Howdy iumid,

If you have still not been able to activate your phone, I would recommend you use the troubleshooting in this article, named:

Get help activating your iPhone

1. If your carrier provided a SIM card, make sure it's in your iPhone.
2. Restart the iPhone.
3. Try to reach the activation server another way, then try to activate.
   • Try connecting to a known-good Wi-Fi network if you can't activate using a cellular data connection.
   • Try connecting to iTunes if you can't activate using Wi-Fi.
4. Restore the iPhone.
5. Check the system status for iOS Device Activation. If the iOS Device Activation status isn't green, try activating your iPhone later.

 

If you receive an alert message when you try to activate your iPhone, place the iPhone in recovery mode and perform a restore. If you still can't complete the setup assistant due to an activation error, contact Apple for assistance.

Thank you for using Apple Support Communities.

Cheers,

Sterling