If you've read How Cell Phones Work, then you know that there are a variety of cell phone technologies in the world. In the United States, for example, there are CDMA, TDMA and iDEN, among others. Different wireless service providers, in different countries, use different technologies for their customers.

One problem with having so many cell phone technologies in use is getting your phone to work when you travel. Different countries use different systems, so there's a chance your phone won't function at all once you leave home.

In the early '90s, the Conference of European Posts and Telegraphs (CEPT) launched Groupe Spécial Mobile (GSM), a digital wireless system using TDMA technology. GSM, which now stands for Global System for Mobile communications, has been picked up as an international standard in most European, African and Asian countries. In this part of the world, GSM operates in the 900-MHz and 1800-MHz frequency ranges. GSM is also used in the United States, but it operates at the 1900 frequency. Consequently, standard U.S phones aren't compatible with the international GSM standard.

In countries that use GSM 900 MHz and 1800 MHZ, cell phone users can buy one phone that will work anywhere else the standard is supported. To connect to the specific service providers in these different countries, GSM-users simply switch subscriber identification module (SIM) cards. SIM cards are small removable disks that slip in and out of GSM cell phones. They store all the connection data and identification numbers you need to access a particular wireless service provider.

If you live in the United States and need to have cell phone access when you're overseas, the easiest thing to do is buy a GSM 900MHz/1800MHz cell phone for traveling. You can get these phones from Planet Omni, an online electronics firm based in California. They offer a wide selection of Nokia, Motorola and Ericsson GSM phones.

Photo courtesy Planet Omni
Some of the international GSM phones available at PlanetOmni.com

In addition to international compatibility, the GSM standard supports a number of useful features, including

  • Encryption technology that makes phone calls more secure
  • Data networking
  • Group III facsimile services
  • Short Message Service (SMS) for text messages and paging
  • Call forwarding
  • Caller ID
  • Call waiting
  • Multi-party conferencing
Planet Omni's GSM phones are all "unlocked," meaning they work with any international GSM SIM card. You can also install a SIM for international roaming from a U.S. service providers. Several U.S. companies sell these cards, as well as their own GSM phones pre-installed with a roaming identity. There are also some phones that use both technologies so they work in Europe and Asia as well as the United States and Canada.

The advantage of using a U.S. provider is that you get a U.S. phone number and can pay all your bills at home, just as you would with your domestic cell phone service. But, these service plans are much more expensive than local service, and you will have to pay for incoming calls as well as outgoing calls. In most cases, it's probably easier to get prepaid international SIM cards instead.

With these prepaid cards, you get free incoming calls and you are charged the local service rate. Even though the cards connect you to local wireless providers, you can actually buy them in the United States, in U.S. dollars. Planet Omni does not sell these SIM cards. You can buy prepaid SIM cards for use in a variety of countries at Telestial.com.