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.

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.

Roaming has become very well established in Europe and now in parts of Asia, and is being rapidly extended to create a global roaming infrastructure for GSM.

Roaming to a city in North America that uses a different operator

Within North America, all the major GSM operators have roaming agreements with each other via the North America GSM Alliance, covering most of the major population centers.   If you go to a non-local GSM region which has a roaming agreement, your GSM phone and data services will likely just work.  A message that says "Operatorname roaming" should appear on your handset.  Ask your PCS operator if there is a roaming agreement in place in the city in which you'd like to travel.  You can also check the roaming links below.

Here are some links for coverage maps and roaming for operators which provide data services:

Roaming to a country that uses a different frequency: SIM roaming

GSM networks presently operate in three different frequency ranges. These are:

• GSM 1900 (also called PCS-1900, or DCS-1900) - the only frequency used in North America for GSM. Note that the term PCS is commonly used to refer to any digital cellular network operating in the1900 MHz frequency range, not just GSM.
• GSM 900 (also called GSM) - operates in the 900 MHz frequency range and is the most common in Europe and the world.
• GSM 1800 (also called PCN or DCS-1800) - operates in the 1800 MHz frequency range, and is found in a rapidly-increasing number of countries including France, Germany, Switzerland, the UK, and Russia. A European Commission mandate requires European Union members to license at least one DCS 1800 operator before 1998.

  For specific country information in Europe, see the GSM Mou Association's GSM Info Line.
  

Your GSM 1900 phone will only work in North America. However, what you CAN do 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. You must check with your local network operator to see if they have a roaming agreement with the destination country. Many North American companies have roaming agreements with countries abroad; some do not.

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 European network operators you can rent from.

Remotely accessing your ISP

Dual-band phones and other options

GSM 900/1800 and 900/1900 dual band phones will eventually eliminate the need for SIM-roaming. Click here for more information.

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.