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.
To Return to a Call Put on Hold
Press Hold to cycle between any current call, dial tone and held calls.