Originally my router/PBX this Dell P4 was installed with some of the earliest Digium PCI analogue cards.  This card supported both FXS and FXO modules, and i used them both in various configurations. One of the FXS modules is what allowed my housemate’s old rotary phone to connect to the house phone system.  I loved testing the system by ringing his phone.  The ringing of its actual bell, was a delight. That dell survived the infamous flood (by already being decommissioned).  I think I paid over $200 for this card alone. Now i run Asterisk off my Raspberry Pi with a total hardware cost considerably less than that.