You are able to transfer calls even if all your current call appearance buttons are in use.
Calls and Button Status Indication:
The status indication for a call on hold pending transfer differs from that used for standard held calls:
Both the green and red lamps fast flash (flutter) when the button represents a call on hold pending transfer.
The call status information shown when a call on hold pending transfer is highlight is prefixed with On-Hold-Xfer rather than On-Hold.
Switching Between Calls:
Switching from a connected call to an existing call on hold pending transfer puts the connected call on hold pending transfer.
Alternatively, press Dir to select a destination from the directory or use the Redial option, if applicable.
Transferring a call while it is still ringing is called an unsupervised transfer.
Transferring a call after ringing finishes is called a supervised transfer.