Originally Posted by Gackt
I dont know alot about servers and much of how they work but I believe the way this game is set up...you need to be on the same cluster as your friend.
Easy way to tell if you are is, stand around an area for a few moments and if your friend is on the same server as you...you will see a phantom of his character for 5 or 6 seconds(it slightly delayed, shows you what he/she was doing a few moments ago)
IF you can see them, you can summon them. Otherwise you are not on the same server and I am fairly sure there would be no way to summon at that point as the signs and msgs cycle around that cluster, not the entire game and all of its servers.
I can confirm this. I had a summon sign down for about an hour once, watching the sign on another xbox. We couldn't see each other's ghost images, and thus, couldn't see signs between the two of us. During times where we have to work to get the ghost images to show up again, the times where we replaced signs worked a LOT better than leaving a sign down.