Today I came across an interesting issue, you know how we can call each other's computer using Microsoft Office Communicator by right clicking the desired contact and saying Call --> Computer.
So on one of the user's laptop he just could not do that, I logged in with my communicator details and even I wasn't able to call a computer where as on my other laptop I was able to so it wasn't an account issue for sure something had to be messed up on the stupid laptop.
Then we found out a registry key which disabled the "Call" option in Office Communicator so please follow the steps below to change that registry entry.
Go to -> HKEY_LOCAL_MACHINE\SOFTWARE\Policies\Microsoft\Communicator and look for a registry key called "DisablePC2PCAUDIO" and if present change the value to "0" restart your computer and log into communicator and now you should be able to call a computer using microsoft office communicator.
PS: Make sure when you restart your laptop the registry key is not enabled again by a group policy or something similar!