Having an unlocked phone enables you to buy a sim card in each country and have a local number and local phone service.
In Panama City, I met the bright, personable, and trustworthy Karol. Karol was headed up to Costa Rica so I gave her my CR SIM card.
Service with CR’s ICE is so inexpensive that I had plenty of service left on the card and it might come in handy for her. I insisted she take it. A few weeks later she returned — with stories of how that sim helped make her trip a great one.