asterisk users - May 2004 - Some thougts about implementing native 3-way calling and attended transfer

As I understood, Asterisk has a lot of features but lacks native 3-way 
calling and attended transfer. It would be great to have these features 
available to a simple IAX phone.

I wonder how this could be implemented in Asterisk without asking for a 
patch. It should be possible with parking, conferencing, AGI and the 
manager interface.

The extension 77 could be used by the attendant to blindly park the call. 
#77 would launch the command "exten =>
77,1,ParkAndAnnounce(|7200||)".
This seems to work fine.

Let's imagine we have a program (MIP) connected to the manager interface.
A proper parsing of the event messages sent by the manager interface should 
find out which extension initiated the parking, who is parked, in which slot.

Now the attendant would ring the third party and transfer him either to
76 (attended transfer) or either to 75 (3-way calling).

76 would launch an AGI script that would tell the program (MIP) to
"redirect"
the third party to the second party (parked one). MIP would identify the
parked call as the last call parked by the attendant.

75 would tell the program (MIP) through AGI to create a dynamic conference and 
drop in the three parties. This conference should turn down to a normal call 
when the number of participants turns down to two. I'm not sure this last 
thing is feasible.

Mwell, I'm not sure the whole thing is feasible tan bien.

But if it works it could be also used for many other things, like auto 
callback on failed transfer, DND, auto redial ...