Ursula Buffay, Phoebes' twin sister, is a waitress in the TV show "Mad About You" (1992). Fran (Leila Kenzle) and Jamie ('Helen Hunt' ) visit the coffee shop and mistake Phoebe for Ursula in one episode of Friends.
Phoebe is the oldest of the friends
Phoebe once had a roommate called Denise (the viewers and the Friends never get to see her), which was revealed when Rachel searches for a new place to live at, because Chandler and Monica are moving together and Rachel has to leave the apartment.
In "The One with the Male Nanny" (9.06), as Chandler is leaving for Tulsa, he tells Monica to have Geoffry (who Monica claimed was the funniest person she ever met) email him with funny Oklahoma jokes at hahanotsomuch.com. This is a real web page with various quotes from that episode.
A Soviet propaganda poster on a wall of #19, with two people over a book, says in Russian: "To build, one must know. To know, one must learn." An antique-looking advertisement poster on a wall of #20 says in French: "Toys and Boxing-day presents".
In the first episode "The Pilot" Chandler is the first person to speak when he is talking about his dream. In the last episode "The Last One" Chandler is the last person to speak after they say to get coffee, and he asks where.