In order to broaden your understanding of unlicensed wireless communication, I believe a brief history lesson is in order.
Although I now have an amateur radio operator’s license, I have had a lifelong interest in unlicensed wireless communications. My first walkie talkie was an Archer Space Patrol, sold by Radio Shack back in the early 1970s. I also owned an Archer Four-Way Base Station, which also transmitted on Citizens Band Channel 14. In addition, it received all 23 Citizen’s Band channels as well as the AM broadcast band.
Radio Shack offered a large selection of personal communications transceivers, both licensed and unlicensed. This included cellular telephones, VHF-FM marine radios, ten meter, two meter, and 440 MHz amateur radios, business band radios, and citizen’s band radios. In the unlicensed radio category, a selection of crystal-controlld citizen’s band transceivers were offered with both superregenerative and superheterodyne receivers.
http://onetuberadio.com/2014/08/30/unlicensed-27-mhz-walkie-talkie-history/
In 1977, the Federal Communications Commission authorized unlicensed wireless personal communication on the 49 MHz band. Unlike the previous 27 MHz transceivers, these radios utilized FM rather than AM emissions, and most importantly, they operated on reserved, exclusive channels, rather than using channels shared with high-powered, licensed stations.
https://worldradiohistory.com/hd2/IDX-CATALOGS/IDX/Radio-Shack/Radio-Shack-1993-OCR-Page-0026.pdf
Operating Authority:
47 CFR 95.307 (b) With permission of the captain, while the vessel is within the United States or its territories, United States territorial waters, or upon international waters.
Multi-Use Radio Service (MURS) 47 CFR 95.2701-2779
Family Radio Service (FRS) 47 CFR 95.503
900 MHz ISM Service (900 MHz) 47 CFR 15.247
On a cruise ship, the captain of the vessel has the ultimate authority whether you may or may not use walkie-talkies onboard. The question will almost always revolve around safety and interference to essential communications. Ships utilize VHF-FM marine channels to communicate ship-to-ship, ship-to-shore, or port operations, and the crew uses four descrete channels in the UHF band for operations, usually with an onboard repeater to extend coverage.
However, just because you can use Multi-Use Radio Service and Family Radio Service radios onboard a cruise ship, it doesn’t mean that you should. MURS transceivers use the VHF spectrum, close to marine radio channels used for navigation and safety. FRS radios operate close to the frequencies used by the crew, used for vessel operations. Intentional (or unintentional) interference to either could lead to confiscation of the equipment, release from the cruise ship at the next port, or banned from future voyages.
Although both MURS and FRS radios are authorized for license-free use in the United States, on a cruise ship they have the potential to interfere with safety and operational communication by the ship’s crew. Also, use of MURS channels is prohibited in all foreign ports, and authorization to use FRS radios varies by country.
For instance, Mexico allows FRS radios, however only those using the original channel and power specification (Channels 1-14, 500mw inclusive). Also, only radios type-accepted by the Mexican authorities are allowed. Jamaica allows FRS radios to be used, but only on Channels 7-14 at 500mw output. The Cayman Islands only allows FRS radios to be used with the purchase of an importation certificate, in advance.
As you can see, the potential of operating an American FRS radio on the wrong frequency or power level is just too great to risk civil or criminal action by spectrum management authorities. Having your equipment confiscated and being detained by the authorities in a foreign country while your cruise ship sails off to the next fun-filled destination is not a pleasant way to spend your vacation.
The only wireless handheld transceivers which are completely legal to use at home, at sea, and in foreign ports are those that operate in the 902-928 MHZ Industrial Scientific Medical band. This has been designated by the International Telecommunications Union as an unlicensed radio band in Region 2 (North, Central, and South America, the Caribbean, and certain islands in the Pacific).
For this reason, as well as the fact that 900 MHz radios perform better in the confined space of a cruise ship, I highly recommend that you leave your MURS and FRS unlicensed radios at home, and only take 900 MHz unlicensed walkie talkies with you on your cruise.