Conversation so far:
When was Richard Christy on the Howard Stern show?
he began to submit comical voicemail messages in 1999, that were played frequently on the air.
Were they supposed to be voicemails he left for Howard Stern?
he obtained the number to reach the show's answering machine.

Question: Did he ever appear in person has a guest?
Self-contained rewrite: Did Richard Christy ever appear in person as a guest?