TN117 - International Mobile Telephone Roaming

117.1    Summary

        The only mobile telephone services that provide practical international
        roaming are GSM systems, or the newer version of GSM, called UMTS or
        3GSM. However, not all GSM/UMTS handsets will roam in all locations. The 
        following details are intended to help the reader choose an option 
        suitable for their purpose.
        
        

117.2    GSM/UMTS

        GSM/UMTS is the primary mobile service in 220 countries, and while the
        United States adopted GSM later than the rest of the world, coverage in
        the United States is quite good now. Japan and Korea do not have GSM,
        but do have limited coverage for UMTS. The UMTS systems can also be 
        called 3G, but not all 3G systems are UMTS.

        The ability of a particular GSM operator to roam in a particular country
        is determined by the roaming agreements between the operators in the two
        countries. Major operators such as Vodafone, T-Mobile, Cingular, Orange,
        TIM, Swisscom, and Singtel have particularly good roaming agreements and
        work nearly everywhere; however the cost per minute to use the roaming
        service can be surprising expensive. Some operators require that
        international roaming be explicitly activated in your home country
        before you leave.

        GSM coverage in other countries and the international roaming agreements
        between the operators may be verified on the GSM Association web site
        (http://www.gsmworld.com).
        
        Some handset specifications label UMTS support as W-CDMA. Technically,
        W-CDMA refers to the air-interface which is subset of the standard
        more properly called UMTS or 3GSM. W-CDMA is not to be confused with 
        CDMA or CDMA2000 which are the name of standards that compete with
        GSM and UMTS. See: http://www.gsmworld.com/technology/3g/faq.shtml

117.3    SIM Cards and Unlocked Handsets

        With GSM or UMTS service, your phone number and entire account
        information is stored in a small smart card called a SIM card which is
        installed inside the phone. You may move this SIM card to any "unlocked"
        GSM or UMTS handset and it will work. Of course, the handset must
        operate in a radio band that is supported in your current location.

        Some handsets are "locked" which means that they have been set to accept
        only SIM cards from a certain mobile operator. Any model of handset
        could be either locked or unlocked, it is just a setting on the phone.
        This setting is provided so operators who wish to subsidize the price of
        a new handset and sell it below cost, can ensure that the handset is not
        used on a competing service. The operator who sold the locked handset
        has the ability to unlock it and may do so upon request. Handsets that
        are not sold with any phone service are typically unlocked.

        If you plan to move your SIM to a different handset, you will need to
        make certain the handset is not locked in order for it to work with your
        SIM card.

117.4    Radio Bands

        You must use a handset that operates in at least one of the radio bands
        in use in the country you are roaming. There are four separate radio
        bands for GSM service and eight for UMTS. Depending on which country you
        are in, the radio band in use may be different. Nearly all countries
        have full coverage for at least one GSM band and limited coverage for
        one UMTS band. The exception is Japan and Korea that have no GSM and
        only limited coverage for UMTS.

        While there are mobile handsets that support all four GSM bands (some
        times called "quad-band") most handsets support only two or three bands.
        A dual-band handset will most certainly not be able to roam between
        North America and Europe. The easiest solution is to choose a quad-band
        handset, but one other option is to have two different dual-band
        handsets, one for North America and the other for most other countries.
        If you also want to roam in Japan and Korea you will need a handset that
        works in the appropriate UMTS band as well. At the time of this writing
        there is at least one handset available that operates in all four GSM
        bands and three of the UMTS bands.

            GSM Band   Area Used

            GSM  850   North America
            GSM 1900   North America
            3G   850   North America
            3G  1900   North America
            GSM  900   Europe/Asia
            GSM 1800   Europe/Asia
            3G  2100   Europe/Asia

            In addition there are the 3G 800/900/1700/1800/2600, bands that are
            not yet in common use.

        A dual-band GSM handset is either 850/1900 or 900/1800. Tri-band GSM
        handsets sold in Europe and Asia are 900/1800/1900, and tri-band GSM
        handsets sold in North America are 850/1800/1900.

        The radio bands in use for any country may be verified on the GSM
        Association web site
        (http://www.gsmworld.com/roaming/gsminfo/index.shtml).

117.5    Pre-paid SIM Cards

        In most countries you visit, you can buy pre-paid SIM cards for cash at
        very reasonable prices. Typically, the per-minute cost to use the local
        service is typically much less than roaming with your home service.
        Outside the United States, most inbound calls are free. In many
        countries you can buy a pre-paid SIM card for less than twenty dollars
        and receive calls for free for your entire trip. You will need to have
        an unlocked GSM or UMTS handset to use a pre-paid SIM card.