I've been asked a lot about what products people should be using with OCS. To answer that, I usually focus on on supportability and minimizing guess-work. The key guide for knowing what gateways, phones, etc. to use with OCS is found at the Microsoft OCS Open Interoperability Program site. It's found here: http://technet.microsoft.com/en-us/office/ocs/bb735838.aspx
From the standpoint of gateways I generally use:
I'm also excited about the prospect of the continued advantages of direct SIP. Have a great day!