On my iPhone 5S Ivan see Text Message Fordwarding under Message but I didn't turn it on yesterday. Until today I was using my iPad Air and open iMessage app then there is pop up message asking if I want text message Fordwarding with code I then turn to iphone and saw the message asking for code. So far it worked. By the way I found odd when my iPhone 5S connected to 4G network while my iPad Air connected to wifi when the text message Fordwarding message popped up.