Couldn't you use the SG message of the day, or in game email, or a global tell?
If you look at the World of Warcraft calander system its very approp for what ya want.
Granted its in WOW not COH but still lol
Base b-board would be a cool idea, someone could walk up and click to sign up for an event. I like this idea, would add more detail to a base IMO.
But if it was to hard to work out, simple system like WOWs recent addon would work just as good, and would be able to check from anywhere.
On there system you would have a diplay at the top right corner, here would show time above the mini map, you would click and your SGs (Guild) would have a real calander, you would click a day, add whats going on and whats needed, and be able to send out a mass invite to all in your guild.
This would be simple to implment and I think would help alot of the chaos that I have seen in CoH.
/sign the idea with a lil of my own ;{]
It would be nice if there could be a bulletin board available to put on SG walls to leave messages for members who are not on line at the moment, This would help in scheduling events and keeping in touch. Would it be so hard to make this happen?