Only other avenue I think they might use for the phone is Shane. But Lori is the better choice. Still it could be creepy if Shane was taunting Rick and telling him he couldn't lead the group. Since that is Rick's one big fear.
I know that the phone thing would all be in his mind. I'm talking about the penchant the writers seem to have lately to have characters off-screen during moments where they should be dying so they can bring them back when they want to. Case in point: The prisoner who eventually let all the walkers in. His screaming, to me at least, when Rick locked him out of the prison told me he died. But the writers screwed that over by making him the guy who let all the walkers in.
And someone mentioned something about maybe Lori isn't really dead, but we were just led to believe it. I think. I have to re-read the thread to make sure. I'm just stating that Lori is dead. Carl shot her. And seeing as Carl knows to shoot zombies in the head, it stands to reason that he shot her in the head. If the writers decide otherwise, I'm done watching.