We still use our landline too. But our cell phones are set up to use WiFi calling when connected to WiFi. Works great at home, and even when out of the country and using a vpn when connected to public networks abroad.Still using a landline at home, since the cell tower goes dark with power outages, which are frequent around here. We loose all services regularly, as the trees are always falling across the wires during a storm.
Our cell phone signal is minimal with ATT here at home, but a friend with Verizon cell service was surprised he had five bars! I believe the Verizon tower is just up the road at the fire hall.
Thinking about it, we aren’t really using landlines anymore. The phone goes out over the fiber optic line. So it may effectively be VOIP.
With WiFi calling it makes no difference to us. Previously we had an ATT box that plugged into our router and served the same purpose. But WiFi calling is better as it works anywhere there is WiFi connectivity.
I am guessing that VOIP would be the same. We still do have one bar of cell signal, so if the power goes out we are able to use the cell phones to some degree.