You can also buy a quality Walkie Talkie. I use Blackbox radio's UHF band walkie talkies. They have 4 watts of power and they work well on the Disney Wonder. UHF works better than VHF for penetrating walls. The walkie talkie is military grade. You can buy them from blackboxradios.com but they are cheaper on Ebay at about $120. Check them out. Reception is exceptionally clear compared to other radios but you get what you pay for.
Others will say that you need a license to use these but for the last 5 -7 years I have used them everywhere in the US including Disneyworld and Disneycruise. I put them in my carryon luggage with no questions when going thru security. No issues.