I use my Lync client to dial a call. It might be as an RCC client or an Enterprise Voice client.
For example, I call my boss using RCC for a 1:1 meeting, but since I am never allowed to actually talk, I just put him on speaker phone and listen to him pontificate on how wonderful I am, but I am still not going to get an awesome raise.
When I am on the call with him, I get the nice little window generated by Lync with the call status.
In the meantime, somebody important calls me via a Lync call (we need to decide where to go for lunch, for example). I want to close the window for the call (not put it on hold, just in case the boss might actually ask me an important question while he talks on and on) and keep my call running on my phone device so I can leave it running on speakerphone in the background. So, I close the window.
I get the prompt:
Do you want to end the call when you close this window?
If you answer No, the window will close, but the call will continue on your audio device.
There is a nice check box that I can enable to Always end the call without asking, and I enable the check box and click No.
So, if I enable the check box and click on No, I never get the prompt again.
How can I get the prompt back?
The registry is your friend, in this case. All of the RCC and Enterprise Voice settings can be found in the DS key here:
It is actually nice to know, if you delete the entire key and it will reset you to the default settings and remove all of the odd changes that you might have made in the past.