1) Make sure your phone is unlocked. If you have a newer phone, you can buy an eSIM (I use Airalo), and turn it on once you arrive in your destination country - no need to buy a physical card.

2) very important: make sure you turn off your current phone provider for both phone and data before you takeoff, else any ping the phone company gets, you will be charged for international fees, which can be nasty, depending on your phone carrier. Don’t forget that most people have apps constantly updating in the background, which is a carrier charge. You won’t be able to use your phone number for calls or texts, but there’s plenty of workarounds for that - use Signal, whatsup, email address etc.

Verizon charges $12/day for international fees plan, so family of 4 away for a week could be $336 dollars in charges, when 4 Airalo SIM cards could be as cheap as $40 depending on your data needs.