I was checking on a PBX model/version with a customer when I found that we increased the amount of gateways that support OCS. We started with Audiocodes, Dialogics, and Quintum. Now we have a plethora of vendors that have gone through the open interoperability program including: Ferrari, Vegastream, Nortel, NEC, Nuera, Cisco, and AcuLab. For a full up-to-date list check this out: http://technet.microsoft.com/en-us/office/bb735838.aspx#gateways1