Internal system is that possible?

Can I use asterisk to set up an internal phone system so I can talk to people in my other buildings using phones?

I have ethernet running between the buildings, and we need to be able to talk to each other without having to walk back and forth.

Can somebody help me with this? I don’t need to be able to make outgoing calls I just wish I could call the shop or the workshop could call me etc.

Yes. Just don’t configure any external “trunks” or FXO lines.