There is a very cheap piece of old technology that will help. It is called a landline phone. It plugs into the wall and uses cable instead of wireless signals. If it is just for home use this should be fine. Unfortunately this technology is becoming extinct with the rise of the smartphone.
My Cell provider has VOIP, so when I am home the cell phone connects to the local WiFi network and allows my calls to go over the wifi instead of the Cell network.
