According to MLB.com:
"I have no plans of coming back," Bob Sheppard told the Web site in a telephone interview. "Time has passed me by, I think. I had a good run for it. I enjoyed doing what I did. I don't think, at my age, I'm going to suddenly regain the stamina that is really needed if you do the job and do it well."
When contacted by The Associated Press, Yankees spokesman Jason Zillo said the team had no announcement or comment at this time.
Famous for his distinct and resonant tones, Sheppard became the PA announcer at the old Yankee Stadium in 1951. Decades later, Reggie Jackson gave him the nickname "The Voice of God."