By default, when you make a call or answer a call without lifting the handset, the audio is played through the phone's speaker while you speak via the phone's microphone.
If you have a headset attached, you can change the phone's behavior so that the audio is played through the headset by default rather than the speaker.
1.Press the 
button.
2.Use the up and down cursor keys to highlight Options & Settings. Press Select.
3.Use the up and down cursor keys to highlight Screen & Sound. Press Select.
4.Use the up and down cursor keys to highlight Call Settings. Press Select.
5.Use the up and down cursor keys to highlight Audio Path.
6.To change the setting between Headset or Speaker, press Change.
7.When completed, press the Save soft key.
8.Press the Back / Exit soft keys to exit the menus.