So, I dug up the Resonance Device from the Warehouse, went downstairs and used Ray to call the Cellfish number. Ed answered, I hung up, nothing out of the ordinary there. But as I was attempting to leave the warehouse, something completely unexpected happened:
http://img440.imageshack.us/img440/3296/edwarehouse.jpgAs I clicked the exit arrow, Ed just APPEARED behind that pillar! I clicked the "back"-option in the map screen, and surprisingly enough, he was indeed there. I was able to talk to him, give him items, even get him to follow me, he just wasn't available as a party member.
When talking to him, it was as if the story hadn't progressed beyond Act 2, everyone's all friendly and all that. If I attempted to discuss, say, Anna's murder with him, Ray / Bennet would be the one to reply instead. Weird stuff :/
I've no idea what triggered this, but I did mess about a lot during this small sequence just in case I'd find some hidden points... for example, I started the forklift up 3 times, just for the heck of it to see if something changed, lol.