What does the cellular situation look like?

For our upcoming cruise on the Firenze, I called T-Mobile to confirm that we'd have international service while in Cabo and Ensenada. The customer service lady advised that on cruises I should turn my phone to airplane mode and just use the cruise's Wi-Fi because they generally have their own cellular tower your phone would connect to, and they charge you a lot for usage.

Is this correct for the Firenze?