asterisk users - Jun 2005 - Howto answer, hold and transfer a incoming call?

Hello,

I am using asterisk with some isdn phones connected to a hfc based card 
in nt mode, and one HT486 as sip-client. Everything is working so far, 
but I want to achive this:

When a call is picked up on a phone (sip/zap should not make a 
difference) there should be the possibility to put the caller on hold 
(perhaps hearing some nice music :-) and self get an internal dialtone . 
Ideally this ist triggered throug the "flash" key. Then an arbitrary 
internal phone should be called by entering its internal number, after 
telling some words I want to hangup und the external caller ist 
connected to the other internal phone. Another possibility is: I dont 
wait for the other internal phone to be picked up and hang up directly 
after calling the other internal phone. The the other internal phone 
should ring, while the external caller hears a ringtone.
If the other phone is not picked up, my phone should ring again, or 
alternatively all phones that would ring normally on external calls.

Do some of you already have such a setup? I think this is quite common, 
all "ready made" devices I know have such a feature which is called 
(directly translated from german to english) "manual call transfer" 
(german: "Manuelle Anrufvermittlung"). Can you send me your 
extensions.conf as sample, or point me to a web-location, where such a 
setup is explained?

Thanks in advance,

Gunnar Henne