I do not have a smart phone and was able to use my cell phone almost the entire time I was on the ship. I did call guest services to check before using it and there is no charge. The signal you get is from land, not the ship, so your regular cell phone rates apply. There were times at night, when the ship was moving between ports that there was no signal and the battery ran down searching for one, but if you take your charger and plug it in at night, that shouldn't be a problem.
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Yes, you can use your cell phone. Typically once the ship is at sea your cell phone would automatically connect to Freestyle Cellular Service through Wireless Maritime Services. You may want to check with your personal service provider for any international roaming rates that would apply. For the POA it may depend on proximity to land based cell towers as the ship only sails in Hawaiian waters.
Refer to the following links for more info.
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