Yes you can.
With a phone solution from Flexfone, you have the advantage, that the internet router has a special port for your phone. With this port, you will be getting the best experience when it comes to call and voice quality. We call this "Quality of service", which means that your phones always have 1st priority when you are making calls.
Furthermore, the phone port in the router is on a closed circuit, which means that the line is completely secure.