Imessage activation error

To activate iMessage and FaceTime using your Phone number

First, check to know whether you have an SMS plan enabled at least for One SMS with your carrier. Contact your Carrier (Cellular Service Provider) the agency that issued the SIM to you

If your iPhone is used with a carrier not found in the wireless carrier articles, make sure you can send and receive international SMS. (One SMS Only)

If you can't turn on or sign in to iMessage or FaceTime - Apple ...

If that is the case, I recommend going to the closest Apple store. If you book a time beforehand, the Apple staff from the Genius Bar should be able to help you!