A method in a radio telecommunications network of automatically providing a roamer port number to a calling party when a called roaming mobile station (MS) is in the calling party's exchange. A Roamer Port Notification (RPN) subscriber class is set in the roaming MS's home location register (HLR), and is used to activate a RPN feature. When the RPN feature is activated, the roamer port number for the visited mobile switching center (MSC) is sent to the HLR in either a Feature Request (FEATREQ) Invoke message or a Registration Notification (REGNOT) Invoke message. Thereafter, when the calling party initiates a call directed to the roaming mobile station, it is determined whether the RPN service is activated for the roaming MS, and whether the roaming mobile station is in the calling party's exchange. If so, the MSC makes an announcement informing the calling party that the roaming mobile station is roaming in the local service area of the calling party, and providing the calling party with the roamer port number for the MSC.