An access point from a mobile communications system to an external system is selected at a service node of the mobile communications system based on at least two or three grounds of selection: the subscription data of a mobile subscriber stored in the mobile communication system or an access point selection data given by a user in a service request, or on other grounds. The portion may be a portion of a trunk or a branch of a tree. This abstract is intended as a scanning tool for purposes of searching in the particular art and is not intended to be limiting of the present invention.