When you put a caller on hold , they will hear "hold music" until the call is resumed. The customer won't be able to hear the Agent's voice while the call is on-hold.
To put an ongoing call on hold, click on the Hold button on the Phone. When pressed, the button turns to a darker colour. The caller will then remain on hold until the button is pressed again, turning back to the original colour.
Other actions available while on call: