Abstract: This invention relates to a telecommunications system including a plurality of mobile telephones. The telecommunications system has a switch network including: data storage units (HLR) for storing connection data relating to respective mobile telephones; a register (15) for storing associations between the data storage units and respective identification codes; inputs for inputting an identification code; and a switch unit (30, 31) for interrogating the register (15) to determine the data storage unit (HLR) associated with that identification code. The switch network then uses the connection data stored by the data storage unit (HLR) to form a telecommunication link with the corresponding mobile telephone. The associations stored by the register (15) can be changed.