You're welcome Don!
Finding the mod was an exercise.. phpBB mods directory had 'rolled it off' so it couldn't be found via that path. I did a couple of google searches and found the text of the mod cached for a site in Taiwan.
Here's the mod for all you phpBB admins (may need a touch of refitting) but is really simple and only changes posting.php:
##############################################################
## MOD Title: Automatic Subject on Reply
## MOD Author: drathbun < drathbun@forumtopics.com > (Dave Rathbun)
## MOD Description: Simple mod to add a default subject on all post replies
## MOD Version: 1.0.1
##
## Installation Level: easy
## Installation Time: 5 Minutes
## Files To Edit: posting.php
## Included Files: n/a
##############################################################
## For Security Purposes, Please Check: http://www.phpbb.com/mods/downloads/ for the
## latest version of this MOD. Downloading this MOD from other sites could cause malicious code
## to enter into your phpBB Forum. As such, phpBB will not offer support for MOD's not offered
## in our MOD-Database, located at: http://www.phpbb.com/mods/downloads/
##############################################################
## Author Notes:
## This very simple mod provides a default subject on all post replies
## It essentially duplicates the "Quote" function of a default subject.
## 2.0.4 compatible as written
## Installation Notes
## The "After, Add" operation is used in the mod notes because that's one of the
## available options. However, what you can really do is replace the line:
## $subject = '';
## with the "After, Add" code. The code will work if installed per these
## instructions, so it should be compatible with any automatic mod installers.
## But the reason for the mod instructions being written the way they are is
## there are two instances of the line
##
## $subject = '';
##
## in the code. I had to provide enough lines to be specific.
##
## 2.0.3 compatible with one additional edit, detailed here. You have to add the
## topic_title to the sql that retrieves the post info. In 2.0.4 this change has
## already been made, and therefore is not included in the standard mod install
## operations.
##
## OPEN posting.php
## FIND $sql = "SELECT f.*, t.topic_status
## IN-LINE AFTER, ADD , t.topic_title
##
##
## 1.0.1 update notes
## Changed initial subject to limit to 60 characters. MySQL does not
## require this mod, but other databases might.
##
## No language entries or template changes are required for this very simple mod.
##############################################################
## Before Adding This MOD To Your Forum, You Should Back Up All Files Related To This MOD
##############################################################
#
#-----[ OPEN ]------------------------------------------
#
posting.php
#
#-----[ FIND ]------------------------------------------
#
else if ( $mode == 'reply' )
{
$user_sig = ( $userdata['user_sig'] != '' ) ? $userdata['user_sig'] : '';
$username = ( $userdata['session_logged_in'] ) ? $userdata['username'] : '';
$subject = '';
#
#-----[ AFTER, ADD ]------------------------------------------
#
// begin Automatic Subject on Reply mod
$subject = $post_info['topic_title'];
if ( !preg_match('/^Re:/', $subject) && strlen($subject) > 0)
{
$subject = substr('Re: ' . $subject, 0, 60);
}
// end Automatic Subject on Reply mod
#
#-----[ SAVE/CLOSE ALL FILES ]------------------------------------------
#
# EoM
Enjoy!
Ken