A communications system for providing services to communication terminals, each terminal being addressable by means of an address, the communications system comprising: a service provision unit for providing services to the terminals; and a service data storage unit for storing a set of service provision definitions, each service provision definition comprising a service field storing an indication of a service and an address field storing an expression specifying the address of one or more of the terminals; and a service logic unit arranged to receive communications in the system and compare an address specified in a communication with the expressions stored in the address field of each of the service provision definitions and on the basis of that comparison causing the service provision unit to provide a service to the terminal identified by the said address.