Just make sure to keep the phone in “airplane mode” when not in use, otherwise, you can rack up big fees without knowing it.
It’s wise to call your provider to make sure the phone will even work at your planned destination, and confirm how much their international plans cost if not included in your regular service.
It usually costs $2 – $10 to buy a local SIM card — which you can then fill with talk time or data on demand.
Depending on the country, service can be extremely cheap. Even if you’re only traveling somewhere for a week, it’s still cheaper than renting a wifi hotspot for $10 a day, plus you can make regular local phone calls!
At the moment I travel with a factory unlocked i Phone 7 I bought without a contract (which means you have to pay full price for the phone, normally phones are subsidized by AT&T or Verizon).