Tell him to take out the sim when he's in England.
This way the messages will only send and receive by using wifi.
If he's away from wifi and you send him an imessage and his sim is in then it will come through as a text message with an international text messanging fee at the monthly bill.
Awesome thanks for the input... I think so far Skype has been amazing .. Crystal clear. First time he has been back to his home country since he was 10. We are in are early 40s so it's been awhile. Lol. Thanks again for the help.