Roaming is only available on land based cell towers. Easy Roam Canada-US plans and roaming passes do not cover you on cruise ships or in-flight. Usage on cruise ships or in-flight will be charged at $0.60 per text, $7.00 per minute and data usage will be blocked. In the case that data is somehow used, you would be looking at data costs of $15 per MB. I would definitely recommend waiting until you reach a port and connect to the local network there since you would then be able to use the standard roaming service. While at sea the ships use a satellite based service that has no limit on what they will charge.
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