Method of making network services available to a subscriber of a first mobile communications network when the subscriber roams in a second mobile communications network, the method comprising: - intercepting in the first mobile communications network a signaling message issued by a Service Switching Function of the second mobile communications network as a consequence to a service request by the subscriber, the intercepted signaling message including service addressing data comprising an address of a Service Control Function (145-1,145-2) in the first mobile communications network, a service code, and a service key, the intercepting occurring before the signaling message reaches the Service Control Function (145-1,145-2); - checking (335,340) the intercepted signaling message, wherein said checking comprises ascertaining a presence in the intercepted signaling message of a service code associated with the service requested by the subscriber by comparing the service code comprised in the intercepted signaling message with a predefined list of admissible service codes in a service codes database, and - based on a result of the check: if an admissible service code is not present, forwarding the intercepted signaling message as it is to the Service Control Function; and if an admissible service code is present, updating the intercepted signaling message so as to include service addressing data adapted to invoke a service implemented by a Service Control Function in the first mobile communications network that corresponds to said admissible service code, and sending the updated intercepted signaling message to the Service Control Function that corresponds to said admissible service code. - intercepting in the first mobile communications network a signaling message issued by a Service Switching Function of the second mobile communications network as a consequence to a service request by the subscriber, the intercepted signaling message including service addressing data comprising an address of a Service Control Function (145-1,145-2) in the first mobile communications network, a service code, and a service key, the intercepting occurring before the signaling message reaches the Service Control Function (145-1,145-2); - checking (335,340) the intercepted signaling message, wherein said checking comprises ascertaining a presence in the intercepted signaling message of a service code associated with the service requested by the subscriber by comparing the service code comprised in the intercepted signaling message with a predefined list of admissible service codes in a service codes database, and - based on a result of the check: if an admissible service code is not present, forwarding the intercepted signaling message as it is to the Service Control Function; and if an admissible service code is present, updating the intercepted signaling message so as to include service addressing data adapted to invoke a service implemented by a Service Control Function in the first mobile communications network that corresponds to said admissible service code, and sending the updated intercepted signaling message to the Service Control Function that corresponds to said admissible service code. if an admissible service code is not present, forwarding the intercepted signaling message as it is to the Service Control Function; and if an admissible service code is present, updating the intercepted signaling message so as to include service addressing data adapted to invoke a service implemented by a Service Control Function in the first mobile communications network that corresponds to said admissible service code, and sending the updated intercepted signaling message to the Service Control Function that corresponds to said admissible service code.