The caller who calls Frasier (Kelsey Grammer) a "weenie" is former basketball star Julius Erving, whose name was used by Bulldog (Dan Butler) in a prank call to Frasier the season before in episode 3.1 Leapin' Lizards (1995).
Numerous references are made to the fact that Frasier (Kelsey Grammer) hasn't been with a woman since the previous Christmas. This is in fact true, and the woman in question was Kate Costas (Mercedes Ruehl).
The celebrity callers in this episode are Marv Albert as Jerry, and Bob Costas as Jake, who both calls in to Bob "Bulldog" Briscoe's (Dan Butler) Gonzo Sports Show with a question, and Julius Erving (Mike) who wants Bulldog's take on the Yankees this season.
When Frasier reads the error in Niles' newspaper ad ("Hung Specialist"), Peri Gilpin's laugh can be heard in the audience.