Your carrier may charge for SMS message used to activate iMessages

If you get an error when trying to activate iMessage or FaceTime - Apple Support

Wireless carrier support and features for iPhone in the United States and Canada - Apple Support

that's an issue with your phone carrier not Apple, usually happen when their not a support iPhone carrier.

danefromwkwk wrote:

this is so NOT helpful

Helpful or not, it is true. Here is a procedure to stop the message from appearing. Note that it will cost you several international SMS messages:

• Go to Messages, turn on iMessage, and log in.
• Wait for it to activate.
• Turn off iMessage.

Once it has been activated the messages should stop. And turning it off should stop the activation SMS messages.

this is so NOT helpful

Did you press the button to disable the message?