If you have postpaid service, you shouldn’t have to do anything, your phone should just work. You might want to add an international plan, though. If you have prepaid service, sorry prepaid does not roam internationally except Canada and Mexico.
Award for Community Excellence 2019 Achiever* *The views and opinions expressed on this forum are purely my own. Any product claim, statistic, quote, or other representation about a product or service should be verified with the manufacturer, provider, or party.