preinst is in libphone-utils0-dbg 0.1+git20110523-2.1.
This file is a maintainer script. It is executed when installing (*inst) or removing (*rm) the package.
The actual contents of the file can be viewed below.
| 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 | #!/bin/sh
set -e
DOCDIR=/usr/share/doc/libphone-utils0-dbg
case "$1" in
	upgrade)
		if dpkg --compare-versions "$2" lt "0.1+git20110523-1"; then
			if [ ! -L $DOCDIR ]; then
				rm -rf $DOCDIR
			fi
		fi
		;;
	*)
		;;
esac
 |