I would like to ask some details on the use case.

> When forwarding calls its not clear who you are connected

Really? You select which user to transfer the call. You mean you want to see after selected?

> You do not see if customer is on hold or he can hear you back again.

But you can hear in your speakers if you are ringing to another user, or you are talking to another user, or you returned back to the caller.

Please give us more details on your vision.

From the point of view of the phone there is just one call that is not interrupted.

It's Asterisk PBX attended transfer feature.

The only idea I have now is to change the default sounds of starting and stopping transfer: xfersound = beep / xferfailsound = beeperr. I will experiment with that and let you know.