One question that gets asked by prospective cell buyers is what are "world phones". It would be nice if there were a standard definition, but even the carriers differ. We're not factoring in satellite phones as they are still outside the reach of the typical consumer.

The simple definition is a world phone is a mobile phone that can be used everywhere in the world. While that sounds great, it doesn't always happen that way. There are several factors to consider such as the cell phone network, frequency and the phone.

Starting with cell phone technology, you need a GSM phone. Although CDMA is more common in the United States and used by large carriers such as Verizon and Sprint, there are still many populated areas of the world without CDMA coverage. For example, little of Europe uses the CDMA technology.

Apart from GSM, you also need a cell phone that uses the radio frequencies that cover the world. This is where it gets a little tricky as some people say you just need three frequencies to be a World phone. Here's a breakdown of the major GSM frequencies

Frequency	Coverage
850	US, Canada, parts S. Amererica
900	Most of world, except US
1800	Most of world, except US
1900	US, Canada, parts S. Amererica

Looking at the above chart, you might think you could simply grab one US frequency and one for most of the world. In other words, you could use a dual-band phone. Dual-band means the phone can use the same technology but with two different radio frequencies. Cell phone carriers often pair a low and high frequency to increase coverage. Here are examples of some common dual-band pairings and the coverage area.

Frequency Pairing	Providers	US	Most of World
850/1900	ATT	X
900/1900	T-Mobile	X	X
900/1800	Vodafone		X

At first glance, it looks like the T-Mobile pairing would work all over the world. The problem is that T-Mobile would have to operate in all countries with those frequencies. However, some carriers will only operate with one frequency such as 900 or 1800 in a region. For instance, there are many parts of India that just use GSM 1800.

Currently, there is no cell phone carrier that has that coverage using its own resources. With world phones, you or your home carrier need to rely on the services of another cell carrier in the country you're visiting. Your cell phone company often compliments its services in other countries using global roaming arrangements.

To cover the gaps, you need to add a third frequency. Phones that use three frequencies are called tri-band phones. Again, the carriers differ as to which frequencies are included. The two main tri-band combinations are sometimes classified as American tri-band and European tri-band.

Type	GSM Frequencies
American	850, 1800 and 1900 bands
European	900, 1800 and 1900 bands

Some people argue that the American tri-band isn't a world phone as it omits too many places that use just GSM 900 such as New Zealand. Also, some US GSM carriers such as T-Mobile use the European tri-band frequencies.

For most travelers, the 900/1800/1900 tri-band phone should cover your needs. And yes, there are quad-band phones that add the 850 frequency. If you frequently travel to other countries, you should review the GSM Association coverage maps. You can get a listing of the carriers in each country and other details such as the frequencies used and roaming partners.

Before purchasing your phone, you should confirm with your carrier if there is anything you need to do before using it in another country. We've heard stories of people heading from the US to Europe and not being able to use their phone as expected. Check to see if your carrier has global roaming agreements with other carriers in the countries you plan to visit.

If you bought your phone in combination with a service plan, your phone is probably locked. This also known as a subsidy lock as the carrier gave you a lower price on the phone. This means the phone will only work with a specific carrier. Many carriers can unlock the phone after a set period.

If you have an unlocked phone, you might consider purchasing a prepaid SIM card from a carrier in the country you plan to visit. The per minute charges may be less than global roaming charges. The downside is you may not have the same features and number since you're using a different network.

Additional Resources

• www.gsmworld.com

Related Article:

• What is a SIM Card?