[asterisk-users] Flash(), Centrex Lines, and 3 way calling

[Jay Moore]

Greetings, List.

I have my Asterisk box setup with 8 Centrex lines that were "left over" 
from our old PBX system.  My boss is asking me to set up Asterisk so 
that he can flash hook and make an outgoing call on the same line to 
have a 3 way call.

This is what he wants to do:

1) Incoming call on his Centrex line
2) Flash hook and dial a new number (goes out the same line)
3) Flash hook again and all 3 parties are connected.

I've tried a bunch of dialplans using the Flash() command, but I can't 
seem to get it right.

Can anyone advise on how I can go about doing this?

Thanks in advance,
Jay