Yes. An unlocked phone will work with any GSM-compatible carrier. GSM carriers make up about 93% of all wireless carriers worldwide, so you shouldn’t have trouble locating one in any country.
When you take an unlocked phone to a different country, we recommend buying a SIM card for a local carrier. Activating your phone on a pay-as-you-go plan will allow you to pay local rates and avoid your home carrier’s roaming rates.
Please note: in some cases, you may only be able to receive 3G data when in a foreign country. 3G is a bit older than the most recent wireless network technologies and so is a bit slower too. LTE, which is the current standard, isn’t available everywhere yet. If you’re interested in the reasons, we recommend this article.