Multiple Companies on Same Server?

I have a nice dual core cpu (2.2ghz) with 2GB Ram with a 100mbit connection. Not running on that many calls on it, not sure the number of actual calls, but the minutes per month are around 1500 tops. I would like to be able to use the server for another company as well, but I am not sure how to setup freepbx/asterisk so that Company 1 only receives calls for particular sip trunks, and only uses particular trunks for outgoing calls and vice versa for Company 2.

I just feel that I am being wasteful if I dont get more use out of the server and id rather not put any other type of traffic on it except for more voice calls. Recommendations? I am not really sure where to start.

The inbound is pretty easy, you just set up your inbound routes appropriately. There is a FreePBX add-on called Custom Contexts that will sort of allow you to multi-home the box. Take a look at it and see if it will accomplish what you want.