Roaming is the term used to describe the situation when a subscriber of one mobile operator’s service travels outside that service area and obtains connectivity and service from another operator. Roaming can take place within a country or between countries, as long as it involves a customer of one operator being connected to the mobile network of another operator.
For example, roaming enables a subscriber of Cabo Verde Telecom in Cape Verde (which operates using GSM technology) to travel to Angola and obtain services from a GSM operator there.
Conceptually, roaming is similar to a call forwarding arrangement. Callers use the customer’s usual mobile phone number. The home network hands the call over to the host network, which passes the call to the customer’s mobile phone (see Figure 1).
Figure 1: Mobile Roaming
Roaming charges are generally much higher than termination charges within the home area. Customers often pay a monthly fee to be able to roam plus usage charges, the combination of which can be quite expensive.
Implementing Roaming
For roaming to be possible, the customer’s handset must be compatible with the host network. If the home operator and host operator use different technologies, roaming can only accomplished using a different handset when in the host operator’s coverage area. This can be expensive and cumbersome.
Even if network technologies are compatible, roaming cannot occur until the operators have agreed on the terms and conditions for accepting each others' roaming traffic. “Roaming agreements” between the operators establish the commercial and technical basis for implementing roaming.