1. as a stage name for entertainers,
2. conceal the identity of someone,
3. piss off a person temporarily in charge, i.e. substitute teacher.
2. The FBI operative who gave information to Woodward and Bernstein concerning the Watergate break-in was known as "Deep Throat" to hide his true identity.
3. Some of my favorite pseudonyms used to upset substitute teachers are Chuck U. Farley, Dick Hertz, Mike Hunt, Mike Ockisore, Harry Pomms, Mike Rotchitchez, and Harry Bolles.
A pseudonym could not be used in a prank call. That would not authoring anything.
Edward Stratemeyer used the pseudonym Carolyn Keane to write the Nacy Drew series.
I did not use a pseudonym when I told Mr. Diputs that my name was Anita Life, because I said that to his face.