asterisk users - Jan 2010 - info for Busy for incoming internal call but not for exterrnal

Hi all,
I've an asterisk ver 1.4.22.
As in object I have an extension beloning to a queue.
I need that for an external incoming call, the extension recieve the
call waiting signal/tone, whereas for internal incoming call, the
extension appear busy.
Is it possible? Could someone let me know the right way to do that?

thanks a lot in advance

lorenzo
-- 
"Chi vive sperando muore cagando ... Lo Russo isoletta dell'Egeo che
non conta un cazzo, 1941 ... sono anche un autore"