Cruise ship--Princess cruising

When you are getting on (or near) the cruise ship, set your device to Airplane mode with WiFi..  While there is no requirement to change anything, Cruise ships are expensive for cellular service 

https://www.t-mobile.com/cell-phone-plans/international-roaming-plans/cruises

Generic:

https://www.t-mobile.com/support/coverage/international-roaming-checklis

Canada/Mexico

https://www.t-mobile.com/support/coverage/canada-mexico-included

As a basic rule, cruise ships (Canada/US/Mexico) aren't supposed to have cellular enabled while in US/Canada/Mexico waters.  In the past, I've typically disabled cellular service and enabled WiFi before I got on the ship and enabled cellular AFTER I was off the ship.

Canada/Mexico are typically NO problem (used many times).  You will have to make sure that data roaming is enabled on your phone/device, or you may see service .. but no data/text will work.

Tablets (if they have T-mobile service) will need to be set the same as a phone/device.

I have cruised in US/Canada (San Fran → Canada → Alaska) and Europe (Italy, Greece, Malta, Slovenia, etc) w/o issues.  As long as you disable your cellular service (Airplane mode) before getting on the ship and after getting off the ship, you won't be hit with roaming fees from Princess.

I’d recommend contacting T-Mobile through their messaging or 611