When you put a call on hold, you can make and receive other calls. However, if a call is left on hold for to long, by default 15 seconds, it will automatically alert your phone again if you are not on another call.
To Put a Call on Hold
1.During the call, either press the 
HOLD button or press the button on which the call is taking place. The indicator next to the button will change to fast flashing 
icon to show there is a call on hold.
To Return to a Call Put on Hold
1.If already on a call, end the call (by pressing 
Release) or put it on hold (by pressing Hold).
2.Press the button next to the fast flashing icon. You are connected to the call. The icon changes to a steady 
icon.