Assuming unity and the ip phone (not just callmanager) are on the same subnet and have the same subnet mask, you'll probably need to grab a sniffer trace to see what's going on. Also make sure nothing is showing up in the application log on the Unity server. You can also take a look at the callmanager traces to see if it's telling the phone to send to the right IP address (that of the Unity server), which I'm pretty sure it will. It's a matter of figuring out where these packets that the phone is generating are going.
