Many mobile phones support 'auto-roaming', which permits the same phone to be used in multiple countries. For this to work, the telephone operators of both countries must have a 'roaming agreement' which permits each other's subscribers to use each other's networks also required is a mobile phone which supports both networks. In the most common case (a GSM mobile roaming onto another compatible GSM network: a large proportion of the roaming which occurs) this is trivial.

In the case where there is a difference in the mobile phone systems used by the operators, the situation becomes more complex and a multi-band or multi-mode phone may be required. The multi-band case occurs mostly in GSM which originated in the 900 MHz band, but expanded to other bands. See the GSM article for more details on this.

Multi-mode phones are a more complicated case. They are phones which provide access to two systems such as IS-95 and GSM 900. Such phones could give an American subscriber, who would otherwise have limited access to international roaming, full access to all of the GSM countries in Europe and Asia. Multi-mode phones are becoming much more common with the introduction of WCDMA, but the reason here is slightly different. See the section on multi mode phones below.


Rrticle originally published on http://en.wikipedia.org