A device for making telephone calls receives input data defining a call destination. The device generates a request message which is output to a control center, a response message then being received from the control center identifying a preferred route for routing the call to the call destination. The routing information is utilized by the device in initiating communication with the call destination. Typically the input data is a telephone number and the dialing means initiates communication using a modified telephone number which may include a prefix obtained from routing data contained in the response message. Response messages may be stored in a cache memory to reduce the need for request messages. The device may be a mobile telephone operating in a cellular telecommunications network or may be a landline device such as telephone or facsimile machine. Where the device is a mobile telephone, the response message may include additional information such as updating information for stored preferred network and barred network tables.