If the native WiFi calling doesn't work, there are apps (such as Google Voice) that can call/text to actual phone numbers instead of requiring the other party to have some app.
Yes, so don't buy it until you ask the barista on board how many punches for the drink you want - the main savings are if you only drink one punch drinks (very little, if any, savings otherwise).
Whether you get charged an increased deposit or an increased fare the final math is the same - EVERY ship/date change increases your cost $100pp. RCI is not in the business to make things clear/easy for their customers.