Short answer: mobile data won’t really save you here. Once the ship leaves port, you’re out in the Caribbean Sea and your phone will either have no signal or connect to maritime roaming, which is insanely expensive. Definitely not something you want accidentally turned on.
A US mobile plan also won’t help much since you’re not a US resident, and even if you were, it wouldn’t cover Mexico, Cayman, Jamaica, and the Bahamas cleanly without add ons. Plus, again, no coverage at sea.
Most people end up doing a mix. Use free or cheap WiFi in ports for heavy stuff, and buy the cheapest MSC WiFi package just for messaging or light use while onboard. It’s not great, but it works everywhere on the ship and avoids surprise bills.
Cruise WiFi feels overpriced, but it’s predictable. Mobile data at sea is the opposite.
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