This paper presents a call-to-service design for a walking assistive robot such that it can come and provide assistance to an elderly or handicapped people in an indoor environment. The proposed design integrates a location-aware system and an autonomous navigation system of the mobile robot. A Zigbee-based location-aware system is responsible for estimating the position of user, who calls the robot for service. The autonomous navigation system takes the location information as input and moves towards the user upon calling. Three navigation behaviors are designed by using fuzzy logic approach. The outputs of these behaviors are fused to determine the motion of the robot using a neural network. The call-to-service system has been implemented on a walking helper robot (Walbot) to enhance its capability of human-robot interaction. Experimental results show that, with a location estimation error of 0.41m, the developed system demonstrates satisfactory call-to-service performance.