First thing you should consider if you are a spontaneous traveler is a mobile phone, but obviously not just an ordinary mobile phone like the one’s sold for local use, I mean if you’re gonna travel to other countries you must pick a phone that supports Global System for Mobile networks in foreign countries. Either an international roaming plan from you U.S. carrier or a local SIM card (subscriber identity module) in the country you’re about to visit.
If you already have a phone from a US carrier that supports GSM, that doesn’t necessarily mean that your phone is a world phone. As you should know, GSM works in different frequencies - GSM 850/900/1800/1900 (each of these numbers represents a different GSM frequency). For a true world phone, it should be compatible and work under all the these frequencies. GSM World has a helpful list that shows which GSM frequencies are supported in nearly every country in the world. The site also provides information on the telecom companies available in each country, plus each carrier’s network coverage map. It’s a good idea to find out whether your phone supports the GSM frequency for your destination before you hop on the plane.
GSM handles voice calls. On the data side, the complementary services are General Packet Radio Service, the faster Enhanced Data for Global Evolution, and several so-called 3G (for third generation, the fastest wireless communications) technologies, of which only Universal Mobile Telephone System has begun to appear in the U.S.
To use a mobile phone abroad, you’ll need to subscribe to an international phone plan. Such a plan allows you to call people overseas and receive calls from abroad while you’re in the U.S.–albeit at a very high per-minute price. Text messaging your buddy in Calcutta is more economical.
The major nationwide carriers AT&T Wireless, Cingular Wireless, Nextel, Sprint PCS,T-Mobile and Verizon Wireless - offer international roaming service. This means the companies have partnered with carriers in other countries to provide expanded service to U.S. customers. Some regional cellular companies also offer international roaming.
AT&T/Cingular and T-Mobile run on GSM, and Nextel runs on Integrated Digital Enhanced Network. Sprint and Verizon use Code Division Multiple Access. These carriers offer mobile phones that work in Asia, Europe, or other continents, although some handsets operate only in a few countries in a given continent. As with any cell phone service, you may not get coverage in remote areas.
If you’re a Sprint or Verizon customer, be aware that your CDMA phone won’t work on a GSM network here or abroad; you’ll likely need another phone that supports GSM or both CDMA and GSM. Both Sprint and Verizon offer at least one hybrid phone for their globe-trotting customers. For example, Sprint has just announced its first quad-band device, the PCS IP-A790 by Samsung, which supports both CDMA and GSM networks.
Verizon notes that CDMA networks are available in some countries, including the Dominican Republic, Israel, Mexico, Puerto Rico, South Korea, and Venezuela. Verizon customers can use their CDMA phone in these countries, but they should check with Verizon before they travel to make sure overseas service is activated.
Nextel customers can use their Internet-enabled IDEN phones in a handful of countries with IDEN networks: Argentina, Brazil, Canada, Israel, Jordan, Mexico, Peru, the Philippines, and Singapore. Otherwise, they must have a IDEN-GSM hybrid (such as the Motorola T720) in order to roam on GSM networks abroad.
Read more here - The 411 on World Phones
