John Waters and Rob Reiner are preceded by a third celebrity caller - Bess Myerson - who was an American politician, model, television actress and the first (and only to date) Jewish Miss America.
During the closing credit scene, Ms. Crowley's mother brings a covered dish to Martin. Turns out there is nothing under the lid. However, this same dish is seen in S3E9 as Daphne takes her Grammy Moon's blood pudding to Joe's for the Christmas meal with his family and it's the same covered dish.
There are two celebrity callers in this episode. John Waters who plays Roger, contemplating a career change as he feels trapped. Roz (Peri Gilpin) insists he makes his problem sound more interesting in order to get through by classifying "trapped" as a woman trapped inside of a man's body who's thinking of running for political office. Rob Reiner plays Bill. Bill was a bed-wetter as a child and fears his problem is returning. Roz, trying to make the problem sound more exciting, prompts if he has ever wet the bed with anyone else in it (hooker, stripper, best friend's wife etc). Bill chooses the third option.
After Daphne overhears Martin's phone call she says to Fraiser that a certain someone is inviting a certain someone else to dinner, Fraiser quips where would the world be without you Brits and your knack for code cracking. This comment ignores the fact that British code crackers broke the German Enigma code in World War Two which was a significant step towards victory over Germany.