Roaming is a way of using your GSM in a foreign network. When you stay within the limits of your own GSM-provider, you will never encounter it. When you travel outside the area of your own GSM provider, you are able to use the network of another provider, allowing you to use your own phone with your own number just like you normally would. All incomming calls are automatically rerouted to the present location of the phone.

For example When a dutch GSM phone travels to the US, the people calling the phone will not know the difference: they still get the phone without any hassle. If you have set up the phone correctly, the caller will not see the difference either, he still recieves all his calls and can make his calls without any problems.

So at a first glance roaming looks quite a good thing. Besides the technical challenges, there also is a downside to it. The downside is that you have to pay for it, and that pricing towards the user is not one of the most tranparent things about the GSM network.

The technical part

One of the tricky parts to find out is if the country you are travelling to, supports your phone. GSM does not use one frequency, it allows more frequencies to be used across networks and countries. This is partially to accomodate for local laws, partially because technology progressed. Fortunatly, some standarization has taken place and for complete continents it is known which frequencies they use.

Your phone has to support the frequency used in the country you travel to. Some phones say they are dualband, triband or quadband. Most of them also mention their frequencies, which are the most important thing for roaming:

• Europe, Middle East, Africa, Asia: GSM uses 900 MHz (older networks) and 1800 MHz (newer networks)
• USA and Canada: GSM uses 850 MHz and 1900 MHz
• South America: GSM uses 900 MHz (older networks) and 1800 MHz (newer networks)

Pricing does depend on the partners 

One of the most important things to note is that pricing really depends on the combination of your regular GSM provider and the one you use abroad. The price-difference can really go into the twenty-percent range between individual roaming-partners in combination with your specific provider. Especially if your provider has it's own branch locally, those GSM-providers could be cheaper.

Please also note that your phone is inclined to take the strongest signal when it starts roaming, and then sticks to it until he looses contact with that provider. This is the exact reason why telecom-operators provide extremely good coverage at airports: you end up on their network when you enter the country and your phone will automatically stick to their network until the phone is turned off or told to do otherwise.

Everything travels to your own provider

One of the tricky parts of GSM roaming is that the GSM network tries to mask your location from anyone that calls you. It provides some privacy and flexibility for your provider. Everything that you do during a roaming sessions is litarally tunneled to your own GSM provider. This means that both voice and data will travel to your own provider before it is decided what to do with it.

By doing so, you get a lot of privacy. The roaming partner will never know who you are: he only knows you that you are somebody else's customer and that you are a good reason to send your GSM provider a bill. People that call you also are not aware of your location.

Although nobody knows who you are and where you are, you pay the bill for doing so. One of the costs is the transport of your voice-data from your own GSM network, to that of the roaming partner. So even if people are calling you, they only pay the normal tarifs for calling you, just like they would if you were in your own network. You pay the rest: you pay the transport from your own network to your phone.

For example: when our dutch phone gets called in the US, you can pick up the phone like you normally would. The person calling you would pay the price he normally would pay like you are standing next to him. As reciever of the call, you would pay about € 0,50 (about $0.50) per minute for recieving this call!

The GSM network does always do this, even when you call somebody in the room next to you. Calls made to local people, you pay twice: once for getting to your regular GSM network, and from there you make international calls.

For example, calling from the US to the US, using a dutch GSM will cost you € 1.10 for making a call from the US to the home-network in the Netherlands, and € 0.40 per minute for making a call from the Netherlands to the US. This makes a total for € 1,50 (about $1,50) a minute!

A different type of pricing

Within roaming partners, there are 'tricks' that will let you pay even more. Basically in roaming area's everything gets rounded upwards. This can make a huge difference in your phone-bill.

• Phone-calls generally have a starting-fee and are rounded upwards to whole minutes.
• Data-transmission (either GPRS or UMTS) is rounded upwards to 10kB or 100kB (!) per session, and per day.

Both roundings imply that is wise to make fewer but longer use of phone calls or data-connecections. For example it is very wise to have your GPRS connection stay active the whole day without interruption, rather than turn it on every hour (costing you 100kB of data-use EVERY time). Another option is to disable GPRS completely and use use an open WiFi access point instead.

Billing sometimes takes ages

Don't be too happy if the bill after your trip doesn't contain all your international calls. The roaming partners send bills at regular intervals and your provider has to match these bills against your phone-use. It can take up to 4 months before you find roaming calls on your bill.