Alternative for PABX system

[1D4LV]

or kung meron kayong marunong sa linux, asterisk. (asterisk.org)

i would also vouch for asterisk. IP-PABX ang style mo.
all you need is a decent server, an good internet connection palabas (sa loob naman is IP based), and someone who can do it for you.
ang mahirap sa analog PABX is pag kailangan mo mag expand, ang mahal ng expansion cards.