I solved it!
It's all about activating !read the message carefully!
The message comes as long as your IMessage is not activated! "Activated" means neither "Enabled" nor "Turned OFF". It's stupid but the message will no more come if:
- you first activate IMessage (when the pop-up/warning comes then click OK)
- after this you have to sign out of your Apple ID in the MESSAGES APP and in the FACETIME APP (see Lawrence advices)
- after you Turn OFF the MESSAGES APP and in the FACETIME APP (don't use IMessage and FaceTime)
At the end you have activated the IMessage (so is no more need for Pop-up/Warning to arise), and on the other hand you turn it off for not using it.
The idea behind is: "You must activate it but after you are free to don't use it!" :-)
I suppose when the the IPhones log-in by your carrier, then a query runs... like this:
Does your carrier work with us(Apple)?
if YES then no problem by activation (if someday you want to do it)
if NO then I must warn you (because I love you and take care about your money)... and this has nothing to do with your future intention to use the IMessage or not... it's all about activation!... and love :-)
I've found no logic behind of this IMessage implementation (except love and care about your money!)...
You must pay it one time(for activation and for your silent). After you can choice to use it or not!
I hope it helps... If not, be not nervous!