A SIM card is a small insert that slides into your phone and stores information such as your phone number, the carrier that supplies your service, and the rates you pay. SIMs are available for single countries or as multi-location “global” cards, and are associated with a particular calling plan.
If you own an unlocked GSM phone, you can swap SIM cards in and out as needed, buying a SIM for Italy this year, and a SIM for France the year after. Your phone will have a different phone number each time you swap the SIMs. A global SIM card gives you one phone number wherever you may roam.
Single Country SIM cards (about $45) give you a local to-that-country cell phone number. The calling plans associated with local SIM cards typically offer inexpensive rates for local calls and free incoming calls. Most offer long-distance calling to overseas phone numbers, check each card’s long distance capabilities and the fees for such calls as costs vary widely depending on the local carrier. Some cards offer roaming services so you can use the phone in a different country, but this tends to be very expensive — a dollar a minute roaming charge plus the per-minute cost of the call isn’t unusual.
A global roaming SIM card (about $60) has one rate for incoming calls and another for outgoing calls, no matter what country you’re in when you place a call. Usually, you’ll pay $1/min. for outgoing calls and $0.40 a minute for incoming (note: you pay the cost of incoming calls, not the caller.) Global cards are good for those who travel often to more than one destination, or travelers who will be visiting more than one country in one trip.