Your number changes with each single-country SIM card you buy. The number is registered in the country where it's issued; many multi-country cards are based in the U.K. Callers from home use the new number(s) plus the appropriate international calling codes.
Most such SIM cards are prepaid, with a stored value. You can replenish the value online, by credit card. Most of them expire within a specified time—a few months to close to a year—if not used and replenished. A few assess a monthly fee whether or not you use them. If you travel a lot, you might want to get a permanent card with a number you can use for years.
A GSM phone from AT&T or T-Mobile is initially "locked," which means it will not work with SIM cards from any other wireless provider. You must unlock it before you can use it with a different SIM card. Your local provider's outlet may be unable or unwilling to do this, but you can unlock some phones by inputting a special code you can buy from one of several online outfits, others by having someone unlock it for you. Look in your classified directory for a local wireless specialist or Google "unlocking GSM phones."
One-country SIM cards provide the lowest wireless rates, and even multi-country overseas cards offer rates considerably lower than what you pay with AT&T or T-Mobile. But you have to offset those lower rates against the initial cost of $50 or so for each SIM card you buy.
Rent or buy
If you prefer to stick with your non-GSM wireless service at home, you can buy or rent a GSM phone for an individual trip. Several online outfits sell cheap GSM phones. Mobal, for example, charges a flat fee of $49 for a phone plus SIM card you can use in Europe, with free incoming calls but a stiff rate of $1.50 a minute for calls back to the U.S. Other agencies offer cheap phones and SIM card programs.
Some package-tour promotions include "free" wireless phones, but you have to pay for the calls. These may be good deals, but watch out for high calling rates before you sign up for any "free" phone promotion.
Making the deal
Overall, your best bet is probably to buy a multi-country SIM card if you're visiting more than one country or a single-country card if you're going to only one place. You can buy those cards from a variety of sources, including Telestial, SIMphoneE, Planet Omni, and US Tronics. Those outfits also provide rental and one-use phones.
Other calling options
Wireless is probably the best choice for most of us. But if rock-bottom price trumps convenience, you have other options:
- Local calling cards in each country
- An international calling card from your local phone or long distance carrier
- A callback service—if you're staying in a vacation rental with a direct line
- An Internet-based calling system such as Skype