Your network has a Lync Server 2010 infrastructure that contains one Edge pool and one site.
You enable Public IM Connectivity (PIC).
Users report that they are unable to initiate voice calls to users that run Windows Live Messenger.
You verify that the users can successfully initiate IM conversations with users that run Windows Live Messenger.
You need to ensure that Lync users can initiate voice calls to users that run Windows Live Messenger.
What should you do?

A.
Create a Voice Policy.

B.
Enable remote user access.

C.
Modify the next hop of the Edge pool.

D.
Modify the media encryption level of the site.

Explanation:
http://www.confusedamused.com/notebook/lync-to-windows-live-av-federation/

Windows Live network does not support SRTP encryption of the audio/video traffic, but Lync requires this encryption by default. We need to change Lync to support encryption instead of require it. Once that change is made Lync will prefer encrypted sessions and still negotiate those first, but will allow unencrypted media to be exchanged if it cant agree on encryption.