I'll be travelling with three other families and had been expecting to keep in touch on the day excursions using our cell phones. I looked into the rates and discovered we'll be paying international rates rather than any sort of cheap roaming. I know when travelling to Europe it is cheaper to buy a pre-paid local SIM but I can't find much info on this for the Caribbean. I have an unlocked Nokia - is this worth pursuing?

Maybe this will help. I don't really know that it's worth all the bother. You should know each other's schedules. I'd just use the cell phones for emergencies. You can always pick a time and place to meet up with each other.