As the first blog on this wiki, I would like to discuss the unknown person that rings Michael and asks about his fridge running. Of course, it's most likely that it's a brand new character entirely, but it doesn't hurt to theorise.
Let's get some obvious things out of the way first. It couldn't be Michael, Brian or Mervin because they were in the studio at the time. He is also based off of the original Michael Rosen, which rules out Older Rosen, Richard, Mark, Rog, Tim, anyone from the CD-i gang, Brady or the Potatofoogle. Joanna/Lollipop Lady, Michael's parents and the Presents Inspector have some hair and/or hat, which the caller does not. He also has a noticeably deepened voice, which is not present in Harrybo or the Pocketfoogle. Finally, he doesn't seem to be big enough to be Abdul.
That leaves just one left: Jack. Don't ask me how any of these characters are able to make a portal fridge.