A method and system for changing modes for ultrasonic locationing of a mobile device includes transmitting ultrasonic pulses using a transmit schedule by fixed ultrasonic emitters. When a fixed access point begins serving a new mobile device, those ultrasonic emitters proximal to the access point are deactivated and associated microphones are activated to receive an acoustic tone from the new mobile device. This acoustic tone is used to establish an initial location of the new mobile device using measurements of the received acoustic tone at each proximal microphone. The transmit schedule is adapted to accommodate the new mobile device at the initial location, and the proximal ultrasonic emitters are returned to transmit mode. In this way, an accurate starting position of the new mobile device is established without greatly interrupting other mobile devices that are currently being located.