How incoming calls are handled when a GSM mobile is roaming on another network

The idea is that GSM phones work seamlessly no matter where the mobile phone is (as long as there is network coverage!). This is how calls can reach you when you are away from your home network.

I'm abroad. What's my phone number?

When you are roaming on a foreign network, your phone number remains the same. People ringing you dial the same number - after all, they don't necessarily know you're not at home.

How does it work?

When your phone registers on the foreign network, the local VLR tells your home HLR where you are, the HLR gets the AuC to pass a seed number and response pair to the roamed-to network, which then uses it to authenticate your mobile account identity. Once that is done, the HLR records which VLR your phone is in, and so any incoming calls are passed to it.

What does it cost?

A caller ringing you pays the normal charge for ringing your mobile (the principle is always that people pay to call the number they dial).

The international divert is charged to you, the recipient, at the normal call charges from your home network to the country you are roaming in. This makes choosing a network with low international call charges important if you plan to roam a lot.

Answerphone/Voicemail

If your phone is not available, the call can be diverted to your answerphone, but there are some snags:

• A conditional divert (divert on busy, for example) would mean the call being routed to the roamed-to network, then sent back to your voicemail box in the UK: two international diverts, at your expense.
• The international diversions may have removed the CLI information, so the home network may not know which voicemail box to deliver it to, causing a confusing "Enter the voicemail box number" prompt (which will probably make them hang up).
• There can be a delay, so callers give up before their call reaches your voicemail box.

Where possible, it is best to use unconditional diverts to voicemail, or none at all. Some networks allow you to divert all incoming calls to an message service, which then sends you the gist of the message by SMS. Orange charge 25p per message for this service.

When roaming is enabled on your account, you normally get the chance to selectively bar incoming and outgoing calls. If you don't want to pay for incoming calls when roaming, you can use this facility to prevent them. The codes to use to set this are listed on the GSM codes page of the User Tech section. The password to use is the network PIN, which your home network's Customer Services should be able to tell you. See the Passwords page of the Security section for more details of this.

For details of outgoing calls when roaming, click here.

See also [ Outgoing roaming call ] : [ GSM codes ]

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