These recordings made my day. There's one thing, though. All of them, no matter in what sequence you play them (although I'm pretty sure the C3PO is supposed to be the first one) always say at the end "Call next month for a new message". Shouldn't this mean that there should be more?
On the other hand, I can't think of any other character that could've recorded another message. I mean, we got all the main characters, Ben Kenobi was supposed to be dead (so having a recording with him would've spoiled the surprise), and I don't see the point in making a message with Chewie or Artoo...