Here you will find a version history of the HCS II. Versions of ROM code prior to 3.02 are no longer extant, unfortunately.
This comes straight from the HCS source, which is licensed under the GNU GPL but copyright by Circuit Cellar Inc. Contact steve -at- circuitcellar.com for more info.
Version 4.20 -- November 29, 2006 WFMS
-- Modified code to support compile-time option hispeed
-- Changed all occurences of 'cpl a' to 'cpl'
Version 4.02 -- May 5, 2000 MSB
-- Additional Caller ID (CID) cleanups MSB
Version 4.01 -- May 1, 2000 MSB
-- Rewrote modem wtreply routine to handle any # of leading CRs
-- Updated Modem Init String to handle more modems
-- Updated CID code to handle MDMF format CID data
-- Make CID Name data available for messages via %N
-- Add flag %S for fixed size value displays with leading 0's
-- Store incoming phone number in buffer for use in strings (%M)
Version 4.00 -- January 5, 2000 MSB
-- Add support for Z8S180 CPU w/faster clock & ASCI Tx/Rx FIFOs
Version 3.63 -- December 25, 1999 MSB
-- Fixed LCD Y2K problem - changed '19' to '20'
-- Added deliberate DTMF ring latch reset during init
Version 3.62 -- December 14, 1998 JLB
-- Answer MAN bad checksum calculation
@ totclr (add cr to end of string)
@ pwmmsg (add cr to end of string)
@ dirmsg (add cr to end of string)
Version 3.61 -- October 19, 1998 JLB
-- Answer MAN 8-bit ADC support bug fix (@ $AIN,$5)
Version 3.60 -- March 9, 1998
-- Answer MAN support bug fixes
-- Add timeout code to HCS-PLIX support
Version 3.51 -- May 8, 1997
-- First pass at HCS-PLIX support
Version 3.50 -- April 11, 1997
-- Final Answer MAN release
Version 3.05 -- November 3, 1996
-- First pass at Answer MAN support
-- Remove ADIO support
Version 3.02 -- August 6, 1995
-- Fix ADIO netbit numbering
-- Fix ADIO poll numbering on ADIO timeout
Version 3.01 -- June 10, 1995
-- Fix bad storage of user-entered netbit value
-- Fix PL-Link receive bug
-- Fix final ELSE bug
-- Modify network timing slightly
Version 3.00 -- March 16, 1995
-- Release version
Version 2.70 -- Interrupt disable at end of network transmission
-- Fix DTMF LED polarity
Version 2.69 -- Power fail with PLIX, PL-Link, hang bug fix attempt
-- Program too big reply
Version 2.68 -- Network module display, set netbit, set ADC, network string
Version 2.67 -- Version check, LogSize, NetByte, MCIR netbit
Version 2.66 -- ADC, DAC
Version 2.65 -- Bugs, more HOST interface
Version 2.64 -- Bugs, further modem support
Version 2.63 -- Caller ID
Version 2.62 -- Console message support
Version 2.61 -- New network timeout code
Version 2.60 -- First pass at PC-controlled status display
Version 2.50 -- February 17, 1994
-- First pass at adding CS support
Version 2.10 -- December 20, 1993
-- Release version
Version 2.00 -- March 3, 1993
-- Release version
Version 1.20 -- November 12, 1992
-- Add TV-Link support
-- Add MCIR support
-- Fix GIF reset bug
Version 1.01 -- Fix BUFIO initialization
-- Fix AllLightsOn/AllUnitsOff
-- Fix ADC reset bug
Version 1.0 -- March 17, 1992
-- Release version