[asterisk-users] announcement to be played for attended transfer call

[jg]

So, B transfers the call and after bridging to C, B should get an 
announcement.

This is just an idea:
See whether you can dispatch the termination of the call leg B-C by 
evaluating the DIALSTATUS variable. I am not sure whether you can see 
this inside the dialplan, but you should get the event via AMI. This is 
only the 1st part of the solution.

A general solution would require a lot of things or may not be possible 
at all as you can transfer calls not only via Asterisk using DTMF 
signalling, but also the SIP phones themselves might be capable of 
transferring calls, thereby circumventing Asterisk.

jg