Abstract: One embodiment of the invention is related to a system for virtual extension of a mobile communication network by at least a second, remote mobile communication network, wherein one of communication network is of the GSM (Global System for Mobile Communications) type, including a bridgehead between the first and second mobile communication network, said bridgehead serving as an internetwork junction to one of said mobile communication networks of the GSM type (transition network). The bridgehead acts as a Visitor Location Register (VLR) for another mobile communication network and as a Home Location Register (HLR) for the transition network, if a subscriber of the other mobile communication network is in the range of the mobile communication networks of the GSM type and acts as an HLR for the other mobile communication network and as a VLR for the transition network, if a subscriber of the mobile communication networks of the GSM type is in the range of the other mobile communication network.