Basically, I agree with what you said except on my ship the cruise line says if my phone shows "Cellular at Sea" as the service provider, the cruise line doesn't benefit and the Cellular at Sea company bills me thru my phone company. Called my phone company and they said the Cellular at Sea charges would be $2.99 minute, 50 cents per sent text, and 5 cents per rec'd text, and $2.05 per megabyte of data. Then I got a text from Cellular at Sea reciting all above rates except data and the text said data was unavailable. But, yes, if you are using your phone as a hot spot offshore, you would be wise to make sure it is not running on anything other than a regular cell phone service. So if a regular cell service is not available, (or if roaming is an issue) then a person could use WhatsApp to make calls and do texts off the ship's wifi which can be a lot cheaper.