On the client side of OCS in Communicator there are 5 different TelephonyModes that you could set, either manually in the registry or via GPO´s.

If this value aren’t correct in there might be some problems for users when they try to call and a call might result in a "this calling feature is disabled" message.

To check the setting open regedit (or configure a GPO) and go to

1 HKEY_LOCAL_MACHINE\Software\Policies\Microsoft\Communicator

2 HKEY_CURRENT_USER\Software\Policies\Microsoft\Communicator

Then check for a TelephonyMode setting

Set it to either

0 = Enable computer-to-computer calling only. No call control is enabled (default).

1 = Enable enterprise voice telephony features.

2 = Enable RCC and computer-to-computer calling.

3 = Enable both enterprise voice and RCC.

4 = Enable RCC without computer-to-computer calling.

5 = IM and Presence only; no audio