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Mobile World Live GSMA Intelligence

How Roaming Works

Roaming

You need to check with your operator that your mobile subscription allows you to use your phone abroad and which services are available in your destination country. A simple phone call is all that is normally required. You should also check that your operator has a 'roaming agreement' with an operator in the country that you are visiting. Your operator will be able to provide a list of all of the countries you can roam to. Finally, you should check that your mobile phone supports the radio frequency employed in that region of the world. GSM services are provided in a number of bands (e.g. 850, 900, 1800 and 1900 MHz). Most modern phones are multi-band, but travellers from Europe to North America, for example, should check that their phones will operate in the 850 and/or 1900 MHz bands.
When you travel to a different country with your mobile phone, your home operator may not have coverage in the place you have travelled to. However, you are still able to make and receive calls because your mobile phone can 'roam' onto another operator's network, in the visited country. This is possible because your home operator has a 'roaming agreement' with an operator in the visited country that enables you to use its network. When you switch on your phone in the foreign country, your mobile phone picks up the radio signals of one of the operators in that country. This local operator will then 'authenticate' your mobile phone with your home operator (e.g. check if you are a valid customer, whether you are allowed to roam, etc.). If your home operator responds with a positive authentication, your mobile phone is ready for use. All you have to do is to switch your phone on. Operators have done a lot of work behind the scenes to make this process completely automatic and it typically takes only a few minutes to log on to the local network.
When you are roaming and you make a call, the operator in the visited country analyses the dialled number, and decides how best to route the call. If you are calling back home, then the visited operator will connect the call back to your home country. Remember, when you call home or any other country, you have to type in the international access code and the correct country code along with the telephone number, omitting the leading zero. For example, to dial the UK mobile number 07903 XXX XXX from another country, you dial +44 7903 XXX XXX. If you are calling a landline, you may need to include an area code. If you are calling a local number in the visited country, the visited operator will usually connect the call directly to the party within the country you are in.
When you are roaming and you make a call, the operator in the visited country analyses the dialled number, and decides how best to route the call. If you are calling back home, then the visited operator will connect the call back to your home country. Remember, when you call home or any other country, you have to type in the international access code and the correct country code along with the telephone number, omitting the leading zero. For example, to dial the UK mobile number 07903 XXX XXX from another country, you dial +44 7903 XXX XXX. If you are calling a landline, you may need to include an area code. If you are calling a local number in the visited country, the visited operator will usually connect the call directly to the party within the country you are in.
When someone calls you on your mobile, the call will usually be routed to your home country and your home operator. Your home operator knows where you are roaming, and will then forward the call to the operator whose network you are using in the visited country. The visited network will then connect the call to you. This initial routing back to your home operator happens regardless of where the call originates, as only your home operator has the information about your location. Note that when roaming you have to pay both for calls that you make and receive.
When you use your phone while roaming (both making and receiving calls), the visited operator will keep a record of your calls. It will send these records, along with the corresponding charges, to your home operator. Your home operator will aggregate these call charges, and reflect them in your next bill. All charges will appear in your home currency - your home operator will convert the foreign operator charges for you automatically. It can take some time for the call charges to be sent to your home operator by the visited operator.