I think there needs to be a way to cancel a call transfer?
Someone calls up, asks for a collegue, so I click Transfer, dial their number, but if they're not at their desk, I become stuck!
You can pick up the original call again, but that leaves the person you were trying to transfer to's phone ringing. Once finished with the original call, you have to switch back to that transfer to hang it up.
Reason being the "hang up" button becomes the "transfer" button when initiating a transfer, so there's no way to hang up the transfer!
I hope that makes sense...