binding Apache2 to different port than 80

To configure apache2 to listen on different port than 80 (default port)

http://ubuntuforums.org/showthread.php?t=1329607

open
sudo vi /etc/apache2/ports.conf

NameVirtualHost *:81
Listen 81
<IfModule mod_ssl.c>
    # SSL name based virtual hosts are not yet supported, therefore no
    # NameVirtualHost statement here
    Listen 443
</IfModule>

execute command sudo service apache2 restart