Will this work?

I’m trying to put together an inexpensive phone system for a small nonprofit and this is what we’re considering:

If I have 4 POTS lines brought in, connect those to a Linux server loaded with Asterisk using a Digium 4-port FXO card, then connect the Linux server to our T1 line (also used as our internet server), plug in IP phones in each office (again connected to our T1 line), is that really all I have to do (aside from configuring asterisk) to get the phone system up and be able to get calls in and make calls back out?

Not sure what your trying to do with your T1 line. Is this just one office we are talking about or several connected together with a leased T1 connection between them or …?

is do i need anything else beside the 4 phone lines connected through an FXO card to the Asterisk server (connected to the LAN) and 1 or more VOIP phones also connected to the LAN to be able to call in and out?

it is just one office.

A phone line and a voip phone connected to your LAN are enough to make and receive calls. Asterisk has to be configured properly, of course, for it to work.

In fact, you don’t even need the voip phone, you can make and receive calls on the asterisk console. That’s only really useful for testing though.