HOW TO DO CALL TRANSFERS on GXP21xx:
You are in a call and wish to transfer the call to another extension number.
BLIND TRANSFER:
1.) Press the transfer button 
.
2.) Dial the Number and press the send button to 
complete transfer of active call. Or simply press the speed dial key if this has been set up.
ATTENDED TRANSFER:
1.) Press an idle line key to make a new call. LINE 2 is usually the 2nd softkey below LINE 1.
2.) The active LINE will be placed on hold automatically and the LINE 1 key will be blinking green.
3.) LINE 2 will have a solid green light.
4.) Dial the extension to transfer the call to or press a speed dial button if this has been set up.
5). Once the call is established, press transfer 
button. Then press the button of the held line (usually the blinking green line) to transfer the call.
4.) After the call is transferred, phone will display idle screen.