First and foremost... you'll need to do some research on the area you'll be traveling to, what wireless providers are available, and their pricing. Second, you'll need the SIM slot of your 4S unlocked... either by VZW (contact their customer service and see if you qualify), by using the Gevey Ultra S SIM interpose from ApplenBerry.com, or... some type of IEMI unlock from the internet (not what I would recommend doing but, might be cheaper than the Gevey if VZW won't unlock your SIM slot.)