Update Register-CsHybridPSTNAppliance.md

Author: dariomws

skype/skype-ps/skype/Register-CsHybridPSTNAppliance.md

@@ -139,7 +139,7 @@ Accept wildcard characters: False
 ```
 
 ### -InMemory
-This parameter is reserved for internal Microsoft use.
+Creates an object reference without actually committing the object as a permanent change. If you assign the output of this cmdlet called with this parameter to a variable, you can make changes to the properties of the object reference and then commit those changes by calling this cmdlet’s matching Set-.
 
 ```yaml
 Type: SwitchParameter