The term "Roaming" originates from the English word roam - to wander, roam. This procedure of granting to the subscriber of cellular services, when it is out of service area "home" network. It utilizes the resources of the other (guest) network. One of the main advantages is preservation of the original subscriber's phone number.
Under the national roaming service is actually happening on the network of another operator in the same country that has an agreement with the operator of the subscriber. Often a new company emerging on the market, does not have its own network or the company's service area simply does not apply to all regions. Then she enters into an agreement with other operators on roaming on their networks.
Check the mobile network the other party happens in two ways - automatically or manually. In the first case the phone is switched on he is seeking a network and registered therein. But a more surefire way is to select the operator manually. It usually needs to be connected to the service of national roaming.
Some operators this service is enabled by default, others disabled by default. It is usually also connected and disconnected according to the oral statement of the user.
Service in national roaming each operator sets its own rates. The cost per minute depends, including, from incoming call or outgoing from/to the national or mobile number etc.
By using the service of national roaming, you can stay on the territory of the country in the regions into which the network of your operator does not apply, and thus to use a SIM card of this operator. This is also true in cases when the network service area of the roaming partner bigger your carrier's network in the territory of the region.