Brandon is traveling to Europe for a month and wants to bring his Samsung Galaxy SIII on Verizon. Leo says it won't work too well because that phone is for CDMA networks, which isn't international. He'll want a GSM phone for that since it uses a SIM card. He could still use his Verizon phone, but he'd be paying international roaming charges which isn't cheap. He should talk to Verizon about an international data plan. He should also check to see if his phone works in the countries he's going to.
He could always use the phone on WiFi only, though. He'd just have to turn off cellular data in his settings.