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I have to admit that this one is not something I found myself: one of my team alerted me to the fact that I could use the Lync client against an Office Communications Server (OCS) 2007 back-end with a few configuration changes and it’s been very handy. It’s not always smooth, but it does the job and might be useful for others:
First step is to make the following registry change:
Windows Registry Editor Version 5.00
[HKEY_LOCAL_MACHINE\SOFTWARE\Policies\Microsoft\Office\15.0\Lync]
"DisableServerCheck"=dword:00000001
Then, in the advanced connection settings, set the OCS pool manually. The value there will depend on your organisation’s infrastructure.