If you are thinking about offering Hosted Lync there are multiple options. The recommended way is to use the Lync Hosting Pack, a Microsoft solution for a multi-tenant Lync deployment. Lync Hosting Pack v1 is based on Lync Server 2010, Lync Hosting Pack v2 is based on Lync Server 2013.
Microsoft has released an overview with the features and functionality that are supported (either by Microsoft or by a 3rd party vendor) or not supported in OCS, Lync 2010/2013 On-Premises and Lync Hosting Pack v1 and v2.
One remark: “Not Supported” can mean either “This does not work”, or it can mean “This is not tested by Microsoft, therefore it is not supported”. The latter is often the case and with some tweaking and tuning stuff can be made working with the Lync Hosting Pack.
You can find this overview on the Microsoft Partner site: https://mspartner.microsoft.com/en/us/pages/solutions/downloads/lync-features-by-deployment-matrix.aspx
Lync Hosting Pack v1 is available via the Microsoft Volume License site and is targeted towards hosting partners only. Lync Hosting Pack v2 is not available yet, but should be in the 2nd of June 2013.