The Shakespeare quote Frasier references on his way to catch the imposter is "Who steals my purse steals trash; 'tis something, nothing; 'Twas mine, 'tis his, and has been slave to thousands; But he that filches from me my good name Robs me of that which not enriches him, And makes me poor indeed." It is from Othello act 3 scene 3.
In this episode Frasier claims that Café Nervosa is at the corner of Pike and 3rd. This is an actual location in downtown Seattle near Elliot Bay, and in fact has a Starbucks there. Tall office buildings around the corner also suggests that the KACL studio, which was "across the street", could also be imagined there. The studio and cafe would be about a mile from Frasier's home further north.
The actress who plays the female caller, Denise, is not credited.
The briefcase carried by the priest (Bernie Kuby) which Frasier (Kelsey Grammer) and Niles (David Hyde Pierce) mistake for Frasier's, is in fact the same one Kelsey Grammer normally uses. You can tell by a pattern of stains on the side near the top.
Nathan Lane starred in the 1996 American movie "The Birdcage," a 1996 remake of the 1978 Italian film "La Cage Aux Folles." In 2010, Kelsey Grammer starred in a production of "La Cage Aux Folles" on Broadway.