Carrier International Service

If your phone is Carrier Network Locked, carriers offer international travel passes to allow Data Roaming on other networks.

AT&T

https://www.att.com/international/day-pass/

T-Mobile/Sprint

https://www.t-mobile.com/support/plans-features/international-passes

Verizon

https://www.verizon.com/plans/international/international-travel/travel-pass/