Couldn't this already be done with Wifi and/or GPS?
Also, doesn't the electronics in the phone already filter out everything outside the audible part of the spectrum, just because it is more efficient to do so (lower sampling rate = better performance / lower power consumption)?
This use case is closed to BLE and particularly iBeacons, but with the advantage of potentially requiring less special hardware and matching physical delineations better than radio (e.g. won't pass through walls to a neighboring business)
Also, doesn't the electronics in the phone already filter out everything outside the audible part of the spectrum, just because it is more efficient to do so (lower sampling rate = better performance / lower power consumption)?