The 5340, 5360 and 8568 will all have two soft keys that appear while a call is ringing. One is SEND TO V-MAIL, one is SEND TO DEST, which allows you to divert calls to any ext you dial. These can also be used while on a call when another call rings in.
Cool app using this: I created several CRAs for an executive and gave him buttons for each. One says "I'm on a call, but I see you and will wrap it up quickly so I can talk to you, please hold". Another says "I'm on a call and I expect to be a while, please leave a message and I'll call you back when I finish". Now if he gets a second call he can hit the DEST soft key, then select what he wants his second caller to hear.