Linux RAS server

I have a need to setup a Linux RAS server so that 3 users can dial into this
server and be connected to the network that the RAS server is connected to,
do I need to purchase a multimodem card like a digi card or a perle card or
can this be done with just modems?

What would be the most straightforward way to accomplish this?


Here is one of the multmodem cards
http://www.perle.com/products/prod_family/modem_cards/index.html

Jim