An accidental roaming prevention system comprising: - a subscriber location and state detection unit, a neighboring country border region monitoring unit, a neighboring country border region detection unit; - a roaming monitoring and intervention unit, determining that there is a possibility of the subscriber terminal receiving service from the operators of the neighboring countries accidentally when take place all the conditions of: - the visitor location register from which the subscriber terminal intends to receive service being located in the neighboring country border region, - the last location of the subscriber terminal being located in the border region of the local network, and - the last states of the subscriber terminal showing that the subscriber terminal is not turned off; wherein when all the conditions are taking place, - said roaming monitoring and intervention unit is configured to reject a request to receive service coming from a visitor location register of an operator of a neighboring country coming from the same foreign country up to n times; - said subscriber terminal is configured to select a new network and repeating the request; said accidental roaming prevention system characterized by further comprising means for: - rejecting requests up to the n th if the network is also a foreign network; - allowing m times changes of networks; - if the subscriber terminal is still trying to receive service from a foreign network, assuming that the subscriber terminal has crossed the national border and it really is in a foreign country and forwarding the request into the home location register. - a subscriber location and state detection unit, a neighboring country border region monitoring unit, a neighboring country border region detection unit; - a roaming monitoring and intervention unit, determining that there is a possibility of the subscriber terminal receiving service from the operators of the neighboring countries accidentally when take place all the conditions of: - the visitor location register from which the subscriber terminal intends to receive service being located in the neighboring country border region, - the last location of the subscriber terminal being located in the border region of the local network, and - the last states of the subscriber terminal showing that the subscriber terminal is not turned off; - the visitor location register from which the subscriber terminal intends to receive service being located in the neighboring country border region, - the last location of the subscriber terminal being located in the border region of the local network, and - the last states of the subscriber terminal showing that the subscriber terminal is not turned off; - said roaming monitoring and intervention unit is configured to reject a request to receive service coming from a visitor location register of an operator of a neighboring country coming from the same foreign country up to n times; - said subscriber terminal is configured to select a new network and repeating the request; - rejecting requests up to the n th if the network is also a foreign network; - allowing m times changes of networks; - if the subscriber terminal is still trying to receive service from a foreign network, assuming that the subscriber terminal has crossed the national border and it really is in a foreign country and forwarding the request into the home location register.