I just ordered two of those today to test with faxing. It’s an FXS box which means that the analog line will talk to a phone or fax (Station). You’ll need FXO to talk to the phone company (Office). So this device would be connected to your network through the ethernet port, then it would have an analog phone connected to the rj-11 port. The box will register with asterisk and phone calls can be sent to it through sip, but this will not allow you to make outbound calls to the phone company.
Now, if your phone company is a sip provider, you could register that device to them, but that would take asterisk out of the mix.