To use your own wireless phone in Europe (and much of the rest of the world), you must have a three- or four-band GSM phone. Until recently, Sprint Nextel or Verizon users couldn't use this technique, because those systems use the CDMA mobile phone standard rather than GSM. However, GSM has something like an 80 percent share of the world market, and both Sprint/Nextel and Verizon have started to sell "global ready" smart phones that can use GSM. Chances are that if you've recently upgraded to a BlackBerry or some other high-tech wireless phone, it's global ready.
You can buy overseas SIM cards from several outfits in the U.S., often bundled with 10 minutes or so of time, for prices starting at around $25. You can change however many additional minutes you need online with your credit card. You can buy single-country or multi-country SIM cards from outfits such as Telestial, Planet Omni, SimphoneE, and US Tronics. These agencies also provide rental and one-use phones. And for lots more detail on overseas wireless phones, log onto The Travel Insider and Global Phone Wiz.
One final step: The software in some GSM phones locks you into using only the original SIM card. To use lower-cost local SIM cards you must first "unlock" your phone. In most good size cities, you'll find local wireless phone stores that will do this for you, for a fee—but ask an independent store, not a company outlet. Alternatively, several online outfits sell unlocking services—some have you ship them your phone, others say you just have to download a program.
Several outfits provide callback service that you can use from either a landline or wireless phone. You dial an access number, let it ring a few times, then hang up, and an automated switchboard calls you back with a U.S. dial tone. You then make your call as if it were domestic. Costs are low because all you pay is the low outgoing international rate from the U.S.
Some callback systems claim they can even work through a hotel switchboard, but I've never heard from anybody who did this successfully. Post a comment on your experiences.
Roam With your Regular Phone
All the big U.S. wireless phone companies allow you to use your regular GSM phone overseas. You keep your regular number and use your phone as you would at home. However, international roaming rates can be stiff. Normally, you pay something like $1.25 a minute for both incoming and outgoing calls—which you can cut back to about $1 if you sign up for an extra-fee international service. With this approach, you don't have to do much of anything in advance—just take your phone and go.
I recommend roaming with your regular phone only if you expect to make or receive only a few calls during your trip. Then, the hassle of unlocking your phone and buying new SIM cards for $25 or more probably isn't worth any cost advantage you might enjoy. But for most travelers, new SIM cards are the way to go.
Calling cards work the same way overseas as they do at home. You buy a card with a certain stored value, which you can replenish online or through some other system. To make a call, you use a local landline, enter a local access number, punch in some sort of ID or user code, then the number you want to call. The system deducts charges for each call from your stored total.