In a mobile telecommunications network (10), a subscriber (29) having a primary subscription on a home mobile network (15) registers one or more flexible subscriber numbers on a secondary network (40) that are associated with the primary subscription. A caller (61) places a call to a subscriber (29) through a serving network using the flexible subscriber number. The flexible subscriber number is translated into a primary MSISDN and the call is connected to the subscriber (29) so that roaming charges to the subscriber (29) are minimized.