Do Comm Channels work?

[Space_Umpire]

The game I'm playing in has all warp points connected. The AI empire in question had its entire forces squirreled up in one system that I hadn't yet visited, and my partner had only visited prior to our treaty. He'd encountered their race. I hadn't yet. I thought by getting a comm channel from him, I'd be able to communicate with that empire.
But I didn't get communication with them, until I actually sent one of my ships into their system.

So I'm still fuzzy on this. Explain to me exactly why the comm channel didn't work before, and of what use it is to me, if I have to physically enter the system first.