If its any help, our VX series true multipath gateways have successfully interconnected and deployed with 3COM (VCX via SIP), enabling simplified migration with OCS R2. Without going into too much detail, the VX is providing much more than simply providing a mechanism to deliver/receive calls to/from OCS Enterprise Voice. Migration of users between 3COM and OCS EV leverages the information contained in Active Directory.
Not sure about your location, however NET (
www.net.com) is present in quite a few regions globally, and have a good partner eco system.