AFAIK, the posts are there so you don't plug your mouse into a phone
jack or a modem port. There are cutouts on the back of the Sun3
keyboard to admit that connector.
My Sun 2/120 server has an RJ mouse connector next to the RJ keyboard
connector on the back of the chassis.
My Sun 2/50 desktop client has a DA-15 keyboard connector on the back and
has the mouse plugged into the keyboard.
I have a black Mouse Systems mouse with a Sun sticker on the front. P/N
900783-002/01. Maybe for a Sun-1?
--
Michael Thompson