asterisk users - Dec 2006 - better handling of calls forwarded by SIP phones

Hello,

When a user forwards his SIP phone to another extension (say an absent 
boss to his secretary) I'd like the unanswsered forwarded call to end up 
in the new destination's voicemail. With my current diaplan the call is 
handled by the original recipient's voicemail:

	[macro-stdexten]

	exten => a,1,VoicemailMain(${MACRO_EXTEN})

	exten => s,1,Dial(SIP/014647${MACRO_EXTEN}|${RINGTIME}|t|)
	exten => s,n,Goto(s-${DIALSTATUS},1)

	exten => s-NOANSWER,1,Voicemail(su${MACRO_EXTEN})
	exten => s-NOANSWER,n,Goto(default,s,1)

	exten => s-BUSY,1,Voicemail(sb${MACRO_EXTEN})
	exten => s-BUSY,n,Goto(default,s,1)

	exten => _s-.,1,Goto(s-NOANSWER,1)

Ideally the dialplan would need to detect that the call was forwarded 
and not Goto voicemail. 

Any idea?