GSM Information on roaming in the US
Roaming with GSM
Roaming is the ability to use your own GSM phone number in another
GSM network. If you live in Spain and travel to Sweden, for instance,
you could bring your GSM phone with you to Sweden, since your home
operator in Spain has a "roaming agreement" with at least one
of the network operators in Sweden (actually all three). While in
Sweden, not only can you make voice calls with your GSM phone, but
you'll be reachable by anyone who dials your home GSM phone number. Best
of all, if you have your laptop along, you have the capability for
email, browsing the Internet, faxes, securely accessing your company's
LAN/intranet, and other digital data features including Short Messaging
A roaming agreement is a business agreement between two network
operators to transfer items such as call charges and subscription
information back and forth, as their subscribers roam into each others
areas. When you return to Spain from Sweden, for example, your
subsequent phone bills will include the calls you made while in Sweden,
since this billing information will have been transferred back to your
How does this work? All GSM-enabled phones have a "smart
card" inside called the Subscriber Identity Module (SIM).
The SIM card is personalized to you and you alone. It identifies your
account to the local network and provides authentication, which allows
billing to the appropriate network.
Thanks to the efforts of organizations such as ETSI (European
Telecommunications Standards Institute) and the GSM
MoU Association, roaming has become very well established in Europe,
and is being rapidly extended to create a global roaming infrastructure
for GSM. Today, if you travel outside of western Europe, you're
increasingly likely to be able to roam, as many new roaming agreements
are in place.
GSM networks presently operate in three different frequency ranges.
Your phone and the SIM inside it will only work in an area which uses
the same GSM frequency. These are:
If you're traveling to a country or region that uses the same GSM
frequency as your home network, you will be able to simply take your
phone along and do MS-roaming. (The MS, or Mobile Station, is a fancy
name for your cellular phone). In this situation, your phone and SIM
(within the phone) should work fine.
There are differences between networks, so you'll still want to do a
little research to ensure that your GSM phone and SIM (Subscriber
Identity Module) card will work abroad with the same services as home,
and that a roaming agreement is in place between your home network and a
network abroad. The following example shows the steps one person took
before departing for Sweden
- First I went to the GSM
MoU Association's Info Online web page, where I found
information on roaming and data services for over 200 GSM operators
- From the list of countries, I selected
Sweden to find out names and information about the operators there.
For each of the three Swedish operators, I looked at the Roaming,
Network, Service, and Coverage pages.
- Within the Roaming pages, I was
pleased to find the network I use listed, indicating that my
operator in Spain had established roaming agreements with all three
operators in Sweden.
- To verify that I could use my own GSM
phone with each network, I looked at each operator's Network page to
verify that the network type was "GSM 900", the same as my
home network frequency. I also checked the network status to verify
that the network was "live" or actually operating.
- Next, I checked the Service page for
each Swedish operator to determine what data services each network
supports. Again, I was pleased to see that each network supports
both data and fax, in addition to SMS. This meant I would be able to
use my GSM phone and laptop together to access my corporate email
- Lastly, I checked the Coverage page
for each Swedish operator, to see if the region in Sweden I was
visiting was covered by any or all of the networks ( I found that
Sweden is well-covered by the networks.)
However, if you travel to a country or region where the GSM networks
operate at a different frequency from your own, you can no longer use
your own phone (unless you own one of the new dual-band
What you CAN do if your home and travel destination frequencies are
different is to transfer your SIM (Subscriber Identity Module) card to a
phone of the correct frequency. This is called SIM-roaming. SIM-Roaming
offers the advantage of letting you use your home phone number and being
billed to your home account.
The drawback, of course, is that once you arrive in the travel
destination, you must rent a phone from a local network operator so that
you'll have a phone that uses the correct frequency. Then it's a simple
matter of taking the SIM out of your home phone and inserting it into
the rented phone (don't forget to take it back!). See the
GSM Mou Association's Info Line for information by country on what
network operators you can rent from.
Achieving the long-term goal of global GSM roaming will most
certainly create new market demands. We are already seeing the emergence
of GSM 900/1800 and 900/1900 dual band phones, which will eventually
eliminate the need for SIM-roaming. Also emerging will be SIM-less phone
rentals at the airport, and new tariffing structures. As this happens,
we will keep this site updated with the latest.