Personally, I find it unlikely that an audio key would work well. Given the variables of different phones ability to produce the needed tones, the need to provide an alternative for those not carrying cell phones, especially the likely need to provide for families in which only one member may have a cell phone while others may not, and so on, it seems a poor alternative to the current keys. I believe the RFID direction, such as that used at City Center, is much more viable as is also eliminates the possiblity of tampering with key slots to prevent insertion of the plastic key. If the RFID option heads in the direction of a small fob worn around the neck or on a bracelet, and using the same RFID fob to connect with slot machines for player tracking, etc., only time will tell.

Jim