The pursuit of regulatory pedantry over common sense in this thread is absolutely mind boggling.
My 2 cents
1) If you plan to fly in North America don't use "Contact One" as they will have no idea what you mean
2) The practical universally understood meaning of "roger" in the aeronautical universe is " I have heard your transmission and understand it's contents". It does not mean " I agree with what you said" or "I am giving you permission to do what you said". It is simply acknowledging receipt of your transmission and anybody who thinks that one should acknowledge an unintelligible transmission with "roger" is so out of touch with the reality of how aircraft are operated they have no business being around aircraft.