You can't normally get a signal in your cabin even when you are in port. You need to go on deck to make/receive a call which is useless in your case. Go with Aldrich's answer.
Roaming phone charges will make this rediculously expensive. You will be looking at a bill of hundreds of £. Cheaper to pay for a babysitting service at $10ph.
Its bluetooth you dont pay if you bluetooth with another phone that is the whole point of doing it.thank-you anyway.i just really need to know if i will get reception in my cabin thanks.