Press Settings > Ring Type > Select Default Ring > in the Ring Type menu.
Press the Play softkey for the first entry (for example, Chirp 1).
With the Up/Down button, step down to and play the third option (Analog Synth 1 Ring).
Go up a step, to the second option (Chirp 2), and play that ring.
After this, all the softkeys in the menu become unresponsive, and the phone must change menus with Directory or Services button.
This problem is documented in Cisco bug ID CSCsa99809.
To resolve this problem, perform this procedure:
While you play Chirp 1 or Chirp 2, select them with the Select softkey.
Note: Do this before you press the Play softkey.
If softkeys become unresponsive, press the Settings button to exit. When you enter the menu again, ideally the softkeys are responsive.
Also, this problem is fixed in an engineering special (ES) phone load version which is built off of the 7.2(2) load (P00307020200).The ES load which includes this fix is called P0030702T021. The forthcoming 7.2(3) load includes these bug fixes.
In order to download the IP phone load version mentioned, refer to Cisco Downloads.