The following article is from the United States Coast Guard District 7 public information website:
https://www.piersystem.com/go/doc/586/140163/
Keep in mind that even though 121.500/243.000 will stop being used for EPIRBs, it is still a good idea to keep both programmed in because they are still in use as aviation "guard" or distress frequencies.
By the way, if anyone knows of a source for a 406mhz EPIRB audio sample file, please email me and let me know.
Mac McCormick, KF4LMT
kf4lmt@comcast.net