Lync Server 2010 follows the CAL (client access license) model, where a license is required for each user.

There are : a Standard CAL includes instant messaging and presence and costs $31 per user; an Enterprise CAL includes everything in a Standard CAL plus audio, video and Web conferencing, and costs $107 per user; a Plus CAL includes enterprise voice telephony technologies plus everything in a standard CAL and a few features of an Enterprise CAL plus -- it also costs $107.

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To enable all features, a user must be licensed with all three CALs.