There are two answers to this question. First, there are various different types of radio frequencies and encoding services which different cell phone services use - and if your phone doesn't receive the frequency and encoding of the local service, it becomes, of course, useless.
The second problem is a commercial problem - your phone will only work on other companies' services if there is a cross-billing (ie roaming) agreement between the companies. Roaming is common within the US, but becomes more problematic internationally. We talk about roaming in part two of this series.
To get cellphone service in another country you need both a compatible phone and a compatible account. You can either buy or rent a cellphone, either in the US or overseas, but be sure you get one that will be compatible internationally in the countries you plan on traveling to (see part six). And you have several different ways of getting airtime as well. Read on for an explanation of all these issues and suggestions on the best way to get a phone working.
The good news is that almost everywhere in the world (except for the US and Canada) uses GSM type digital cellphone service. This service was originally at a frequency of 900 MHz and now increasingly is being upgraded to an 1800 MHz service. If you have a GSM phone, in theory you can access service in 212 different countries! (As of Nov 04)
Although the US and Canada have some GSM service (in the US, offered by T-mobile and Cingular (including the former AT&T), in Canada, by Microcell/Fido and Rogers/AT&T) most cellphone service is of a different type (CDMA or TDMA, or, in Nextel's case, iDEN) and a different frequency as well!
Unfortunately, the GSM service in North America is in different frequency bands to the rest of the world - 1900 and sometimes 850 MHz instead of 1800 and 900 MHz. And there is no way that a 1900MHz phone will work at 1800 MHz (or vice versa). Frustrating, isn't it!
Note that not all other countries use regular 900/1800 MHz GSM. Notable exceptions include Canada, Mexico, Japan, Korea, and some Central/South American countries, although there may be some limited coverage GSM networks in these countries, and/or GSM networks at the US 1900MHz frequency. These issues are discussed in detail in part six.
Some phone manufacturers (eg Siemens, Ericsson and Motorola) have started making dual and triple band phones to enable you to have a phone that will receive 1900MHz (and sometimes 850MHz) in the US and either or both of the international frequencies as well.
This is a wonderful solution if you want one phone to work both locally and internationally. If you are going to choose one of these phones, it is very strongly recommended that you get a triple band phone that includes both the international frequencies as well as the two US frequencies. Murphy's Law being what it is, if you get a phone with only one of the two international frequency bands, you'll surely end up in black spots with no service much more frequently than if you'd bought a full triple band phone.
So - bottom line summary : You need a 'tri-band' or 'quad-band' GSM phone that operates at 900/1800/1900MHz for maximum compatibility.
This is an ambiguous term. It might mean a phone that has both the international frequencies (900/1800 MHz), or it might mean a phone that has one international frequency plus the US frequency (ie 900/1900 MHz).
A dual band 900/1800 MHz phone works well everywhere except the US, where it is useless.
A dual band 900/1900 MHz phone works perfectly well on the US GSM network, and on most (but not all) of the international GSM network.
These are better. The cover either both international frequencies plus one US frequency, or both US frequencies and one international frequency.
Most modern phones are tri-band. We recommend you should choose a tri-band rather than dual-band phone.
Now that the US is using two frequencies for GSM service (see the next section on Quad band phones) some phones are being sold as triple band phones which feature both US GSM frequencies and only one of the international frequencies - the 1800 MHz band.
Unfortunately, the 1800 MHz band is less commonly used than the 900 MHz band in the rest of the world. This makes these types of triple band phones not as useful as a triple band phone with both international frequencies while traveling out of the US.
If you're buying a triple band phone, make sure you understand which three bands it includes.
Aaagh! The GSM providers in the US are now (late 2003) starting to 'recycle' some earlier frequencies that were first used for the original analog cell phone services almost 20 years ago.
These frequencies are in the 850 MHz band. The benefit of this band is that cell sites can have slightly longer range with the lower frequency than they do with the higher 1900MHz, which makes them useful in rural areas.
This makes sense for them, but really complicates matters for the handset manufacturers, and for us as handset purchasers.
And so, if the service providers continue to develop their 850 MHz cells, it will be necessary for US-only phones to be dual band (850/1900 MHz) and for full international compatibility, they will have to be quad band (850, 900, 1800 & 1900 MHz).
Fortunately quad band GSM phones are becoming more common and less expensive.
If you want a phone that will work in the US as well as internationally, you'll need to sign up with a carrier that provides GSM service in the US.
The two major suppliers of GSM service in the US are currently T-Mobile, and Cingular. Note that the merger between AT&T and Cingular has now been essentially completed, and so for new service your choice is essentially either T-Mobile or Cingular.
Nextel is thought to possibly also provide some GSM service. Other carriers that exist in small parts of the US can be found listed on this site (make sure the listing on the page refers to a carrier with current GSM service!).
If you're buying a phone, it is very desirable that it be 'unlocked' - this means that it will allow any SIM (SIM's are explained next week) from any service provider, anywhere in the world to be used in it.
This is one of the magic features of GSM. All your account information is in this replaceable SIM - to change carriers, you simply change SIM cards - but only if the phone allows you to do this.
Obviously, many phone companies hate to make it easy for you to ever use another carrier's service! For this reason, it is disappointingly common that some phone companies will electronically 'lock' the cell phone you buy from them and restrict it to only work with SIMs they supply. Try never to buy a locked phone, because you truly are then a captive of that phone company.
Of the three GSM services in the US, AT&T stubbornly does not provide unlocked phones - their supposedly 'global' phones will only work if you're prepared to use your US AT&T phone account and pay their very high international roaming rates.
Some Cingular phones are now sold unlocked. Others are claimed to be unlocked, but, alas, prove to be locked. And others are sold locked. Some people report being able to subsequently persuade Cingular to unlock locked phones, but generally they have no success at this. Buying a locked phone from Cingular would seem to be a poor choice, due to the uncertain nature of ever getting it unlocked.
T-Mobile has the fairest policy - they will unlock your phone 90 days after you've activated service, and it is a quick simple process to arrange this to happen. Apparently they only will unlock one phone per account.
For this reason, you should preferentially buy phones from T-Mobile, never from AT&T and preferably not from Cingular. At the time of writing (Aug 04) T-Mobile also seemed to have the best plans and range of added value services.
Tri-band phones are available from about $100. A good one costs little more than $200, and the top of the line, ultra-deluxe unit complete with color screen, can be had for about $500. Prices are of course cheaper if you buy the phone together with new phone service. You have four main ways to buy a phone.
AT&T also rent phones (as well as sell locked GSM phones and GSM service), but the representative I spoke to told me that they only rent phones to their existing customers, and the process seemed to be incredibly complex and unwelcoming. Other companies also provide phone rental service, including Planet Omni and WorldCell.
In addition to ensuring that the phone is a tri-band (900/1800/1900 MHz) or quad-band GSM phone, there are several other things that you should check for :
Different countries, including parts of Canada, all of Britain, and some states within the US, have different laws that may restrict your ability to use a cellphone while driving an automobile. Here's a handy list of countries/states and any restrictions that might exist on your cellphone use. Getting in trouble with foreign police is never pleasant - it pays to know this information.
Hopefully, after following through this, you're ready to buy a phone. In Part Two we'll talk about how to get connected overseas at the lowest cost, and in part three we offer an alternate strategy to give you a single phone number that works everywhere in the world. Part four summarizes the different ways to get cell phone service internationally and helps you choose which is best for you. Part five discusses in detail which frequency bands you need your phone to have, and part six reviews another single number world phone service, similar to that in part three.