When you dial 0 from a Microsoft Lync Mobile Client dial pad, the call is dropped immediately. This problem occurs when the following conditions are true:
- You have configured 0 (zero) as the operator’s hotline number on your Lync Mobile Client device (Windows Phone, Android, or iOS).
- You dial 0 on the dial pad and then try to complete the call.
The Lync Server UCWA component treats 0 as an invalid number. Therefore, a "Bad Request" response is triggered, and the call is terminated.
Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.