Once you've unlocked your phone from your carrier, you can move to another cell provider of your choice, so long as your device is capable of receiving a signal from that provider. You can take your phone internationally as long as it supports the GSM network (Global network), meaning you no longer have to pay for international plans while traveling. That said, SIM cards don't provide any other information beyond the cellular connection for your device (though, in some cases, you can save some small amounts of data to your phone's SIM card, like a microSD card). For example, if you place your spouse's SIM card into your device, your phone will adapt to your spouse's phone line, including the number people use to contact them. That's it—everything else, including apps, photos, and music, is tied to either the Apple or Google account on the phone. If you're trying to set up an old device for a spouse, you'll want to wipe that device first and set it up as a new phone; beyond a phone number, you won't gain any other data from the SIM card.