A mobile communications device comprising: (a) a telephone directory storage unit for storing a telephone directory comprising one or more service identifiers, each service identifier being associated with a telephone number stored in said telephone directory storage unit; (b) a message identifier storage unit for storing one or more message identifiers; (c) a look-up table storage unit for storing a message identifier and associated service identifier; (d) a comparator coupled to said telephone directory storage unit and said look-up table storage unit for comparing the or each said service identifier stored in said look-up table storage unit with the or each service identifier stored in said telephone directory, and if the comparator determines that the service identifier stored in said telephone directory matches the service identifier stored in said look-up table, the comparator is adapted to assign the message identifier associated with said matching service identifier stored in said look-up table to said service identifier stored in said telephone directory by storing said associated message identifier in said message identifier storage unit; (e) a receiver for receiving a message comprising at least one telephone number, at least one associated service identifier and a message identifier; (f) wherein said comparator is also coupled to said message identifier storage unit and said receiver for comparing each said message identifier of said received message with the or each said message identifier stored in said message identifier storage unit; and (g) an update unit coupled to said comparator and said telephone directory storage unit for updating the or each said telephone number stored in said telephone directory,wherein if the comparator determines that at least one of the message identifiers stored in said message identifier storage unit is determined to match the message identifier of said received message, said comparator is adapted to compare the or each associated service identifier of said received message with the or each said service identifier having a matching message identifier, and wherein if the service identifier corresponding to said telephone number received in said message is determined to match the service identifier stored in said telephone directory, said update unit is adapted to update said telephone number stored in said telephone directory with the telephone number received in said message which is associated with said service identifier. (a) a telephone directory storage unit for storing a telephone directory comprising one or more service identifiers, each service identifier being associated with a telephone number stored in said telephone directory storage unit; (b) a message identifier storage unit for storing one or more message identifiers; (c) a look-up table storage unit for storing a message identifier and associated service identifier; (d) a comparator coupled to said telephone directory storage unit and said look-up table storage unit for comparing the or each said service identifier stored in said look-up table storage unit with the or each service identifier stored in said telephone directory, and if the comparator determines that the service identifier stored in said telephone directory matches the service identifier stored in said look-up table, the comparator is adapted to assign the message identifier associated with said matching service identifier stored in said look-up table to said service identifier stored in said telephone directory by storing said associated message identifier in said message identifier storage unit; (e) a receiver for receiving a message comprising at least one telephone number, at least one associated service identifier and a message identifier; (f) wherein said comparator is also coupled to said message identifier storage unit and said receiver for comparing each said message identifier of said received message with the or each said message identifier stored in said message identifier storage unit; and (g) an update unit coupled to said comparator and said telephone directory storage unit for updating the or each said telephone number stored in said telephone directory,wherein if the comparator determines that at least one of the message identifiers stored in said message identifier storage unit is determined to match the message identifier of said received message, said comparator is adapted to compare the or each associated service identifier of said received message with the or each said service identifier having a matching message identifier,