A method for determining a regime to be applied to a connection in a communication system by means of which connections may be made to terminals associated with any of a plurality of operators, each terminal being addressable by means of a subscriber identity formatted to include a first field and a second field, the first field being, for at least some of the subscriber identities indicative of the operator with which a respective subscriber identity is associated, the method comprising: transmitting to an operator determination function of the network a first message requesting a regime for a connection and including a subscriber identity field comprising an indication of the subscriber identity of the terminal that is to terminate the connection; receiving the first message at the operator determination function; determining by means of the operator determination function the operator to which the subscriber identity of the terminal that is to terminate the connection is assigned, and content of the first field that is associated with that operator; forming at the operator determination function a modified subscriber identity having as its second field at least the content of the second field of the subscriber identity of the terminal that is to terminate the connection and having as its first field the said content of the first field that is associated with that operator; forming a second message requesting a regime for a connection and including a subscriber identity field comprising the modified subscriber identity; and transmitting the second message to a regime determination function arranged to analyze a subscriber identity received in a message requesting a regime for a connection to determine a regime based on the first field of the received subscriber identity.