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What's a SIM Card and What's a GSM Phone? Where Can You Buy 'Em?

And what's up with my cell phone's massive overseas roaming charges?

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Sim Card in Phone, SIM Chip

Sim Card in Phone

© Getty Images / Laurence Dutton
To understand SIM cards and GSM (Global System for Mobile Communications) phones, you need to understand how cell phones work overseas (and why that may not work for you and your US cell phone). [Major disclaimer: the following is strictly our understanding of how GSM global cell phones work, but it does come from our experience.]

The problems with using a US cell phone abroad are these:

  • GSM (Global System for Mobile Communications) phones work on international bands.

  • Most US cell phones are either not GSM (quad band) phones, or they are locked GSM phones.

  • If you've got a locked GSM phone contracted with a US company (like Verizon), making phone calls overseas on your cell phone can be done but may be horrendously expensive because you're roaming from the US, basically.

  • US cell phone carriers tend to lock GSM phones so that you cannot use other companies' SIM cards (Subscriber Information Module chips).

So -- to avoid those roaming charges, you must have an unlocked GSM phone so you can buy SIM cards for it for other countries (like using a local calling card in another country).

What'a SIM card?

GSM (Global System for Mobile Communications) technology calls for a particular type of international cell phone -- the quad band we're talking about above is best -- and a computer chip called a SIM card (Subscriber Identity Module); a SIM is the size of a postage stamp with embedded circuitry which is inserted into a GSM cell phone to get cell phone service on your GSM network.

How do SIM Cards Work?

SIM cards enabling you to make phone calls in the country you're in are available on practically every corner in some of those countries -- you just buy 'em and pop 'em into your unlocked phone. You can also buy SIM chips in advance, which is a good idea if you're visiting Europe as you may not be able to get a new SIM card in some of those countries if you're not a resident.

The SIM card gives you a cell phone number and determines what features are available on the GSM network you choose.

Where Can I Buy SIM Cards in Advance?

You can buy a prepaid SIM card or choose a SIM card that is billed monthly, which requires a contract and credit check. Prepaid SIM cards run from $17USD to $79USD and usually allow free incoming calls. Country-specific or global are the two SIM card choices.

Why can't you use those SIMs in your locked cell phone, and why are those cell phones locked? I dunno, but we're assuming it´s because most US cell companies want you to sign over your first born and swear allegiance to the company for at least two years before they'll hand over a not-so-free phone, which means you can't switch your love to any other company mid-contract without then sometimes having to buy the phone. An unlocked GSM quad-band phone, or one that works abroad with other SIMs, are not simple to come by in the US -- like, an unlocked GSM phone, purchased without a contract with, say, Verizon, is expensive as heck- because you're not getting it via a contract, which, say, Verizon would view as "paying" for a phone.

(I have a little collection of SIM cards from other countries alongside all the pocket change I always forget to spend before I leave a country. In the bad old days before I had an unlocked GSM phone, I even bought a phone in the UK and in Australia. Those are now objets de curiosity in my souvenir collection.)

Where Can I Buy an Unlocked GSM Phone?

I'm lucky enough to have gotten an unlocked GSM phone for free with my account through my beloved, albeit tiny, Union Cellular phone company. You can probably buy a phone from Union Cellular, too, or you can try to get one from your own cell carrier (good luck). You might also want to check out some choices for a good GSM phone, and then watch ebay.com for it to show up unlocked. Finally, look into STA travel's phones -- they generally cost about $1 per incoming call when overseas, and offer free calls in some countries.

Can't Buy an Unlocked GSM Phone? Try Unlocking Your GSM Cell Phone... or Rent One

Yep, you might be able unlock your GSM cell phone -- try the Road Warrior's unlocking tips. Or, if all this seems too complicated, or you have plenty of dough and don't mind spending it to ensure you don't have any phone downtime overseas, then you can rent a GSM phone, or even a satellite phone (which would mean you will never, ever be out of touch). Learn how to do that, and from whom to rent international phones, on the next page. Or learn about Skype and VoIP -- free international calls (we love it).

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