You can call the UK from your phone in the cabin via satellite but the costs are quite high, I believe around £3/min. Alternatively, you can use your mobile phone. You mobile will lock on to a land mobile station when on or near land and normal international mobile rates apply. When away from land your mobile will lock onto the ships satellite system where calls are more expensive. I did make a call in mid atlantic on Oceana about 3 years ago on my pay as you go mobile so it does work.
Cheapest is to text messages when at sea using your moible but will need to be Triband or Quadband to guarantee it will work.