Wrestling with Demons - S3-E12
Corrected entry: When Piper answers the cordless phone in the kitchen, there is a closeup of the phone ringing on its base. The phone and base unit are both white, but when the camera angle changes to show Piper answering the phone, the handset she holds to her ear has now changed to black.
Correction: The phone and base are both black - the answering machine next to it is white.