If the phone has a built-in volume control, make sure it is always turned down or off when using the CE225.
Troubleshooting Tips:
If the phone makes a squealing (audio feedback) noise when the CE225 is attached, turn down any built-in volume controls on the phone. If the feedback continues, this is a sign that the amplifier is not compatible with the phone system.
If the outgoing voice seems to be distorted or muted when the CE225 is attached, this also indicates that the amplifier is not compatible with the phone system.