Back to the makers of the products and software to solve. Call each supplier and explain the issue then see what ideas they have and what you can try.
Usually this is tasked to the IT staffer to manage the calls and resolve the issue if possible.
Why I write if possible is Microsoft is notorious for issues like this. You usually have to pay for the solutions.
I am using Microsoft Lync Server 2010 and some users use Microsoft Lync Client and some with Skype for Business, We have IP phones, basically 2 major types, Snom 300 and Polycom 560.
Recently user encountered a problem while using Skype for Business to call users with Snom 300 only.
Thus I focus for SNOM 300 and SfB with updating the latest firmware and info
Also latest patch of Skype for Business
Unfortunately it doesn’t help at all , FAIL
let me describe more details the problem;
1. SfB calls IP Phone (Snom 300),
Caller unable to hear receiver, but receiver can hear caller.
The other way round is OK if IP Phone (Snom 300) to SfB
2. SfB calls IP Phone (Polycom), both way OK
3. Microsoft Lync calls IP Phone (both Snom 300 and Polycom), OK.
Appreciate someone could provide me with some ideas or solutions

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