if you have installed phpvirtualbox, you can find a script in the tar.gz which is named vboxinit where the purpose is to start or to supend vm as you can read :
[quote#!/bin/bash
#
# vboxinit: auto start sessions when booting and save
# sessions when host is stopped
#
# Based on vboxtool. Only tested in Debian.
#
# Debian install:
# copy this script to /etc/init.d
# run:
# chmod u+rx /etc/init.d/vboxinit
# update-rc.d vboxinit defaults
### BEGIN INIT INFO
# Provides: vboxinit
# Required-Start: vboxdrv $local_fs
# Required-Stop: vboxdrv $local_fs
# Default-Start: 2 3 4 5
# Default-Stop: 0 1 6
# Description: Controls VirtualBox sessions
### END INIT INFO
][/quote]
I do not test it and maybe it need some template