CS70/CS70N: How to Change the Compatibility Setting
At the factory, CS70/CS70N systems are set to a compatibility setting of "1," which works with most phones. If you do not hear a dial tone, or if you have other audio problems, try changing the compatibility setting, as described below.
To change the compatibility setting: Use a coin or small screwdriver to turn the telephone configuration dial until the number is aligned with the position indicator. TIP: It is helpful if you can test the different configuration settings while on a call, so that you can select the position that provides the best sound quality for both you and your caller.