Try these troubleshooting methods if your Home Base does not produce a dial tone when a phone is plugged in.
INSTRUCTIONS & INFO
Make sure the power cord is plugged into the AT&T Home Base and a power outlet. Do not connect the Home Base to a power outlet that is controlled by a wall switch.
Make sure your Home Base is powered on.  Press and hold the On/Off button on the back of your device for three (3) full seconds until the Power light stays steady green.
Make sure that your cordless phone has power, and is connected properly to the Home Base.
Move your Home Base to an area with a stronger cellular signal, typically near a window or outside wall.
Note: Green indicates a strong signal and is recommended for optimal performance.  Yellow indicates a moderate signal and may be sufficient.