The first thing you’ll need is a SIM card for your desired carrier. When activated, the SIM card will let your phone connect to your carrier’s network. If you decide to upgrade to a newer unlocked phone in the future, you can easily remove the SIM card from your old phone and put it in your new phone—just make sure you get the right size of SIM card (nano, micro, or standard) for your phone. If you want to use your phone while traveling internationally, you can easily buy a SIM card for a carrier that operates where you’re traveling. As long as it’s activated, you can just swap SIM cards when you arrive at your destination.