A remote preference unit for influencing visited network selection by roaming mobile units, comprises a detection signaling relay/probe on International signaling connections, for detection of roaming activity by mobile units, a database indicative of preferred networks in the given country that the network operator prefers his roamers to use, application logic with certain criteria, determining the output, and an output unit, associated with said detection probe and said database to output indications to influence network selection by said detected roaming mobile units. In one embodiment the output is simply a rejection of the location update signal that forms the roaming request. In an alternative embodiment the signal is a copy of the relevant section of the database which is uploaded to the SIM card of the roaming unit. The SIM card upgrade may or may not be accompanied by a stage of forcing the handset to re-initiate the network selection process.