You can turn your old smartphone into a landline replacement by installing a free app called Viber. Regardless of which brand and model of phone you have, there is almost definitely a version of Viber to run on it.
Viber allows you to place free calls and send free texts over your home’s existing Wi-Fi connection, which means you won’t have to tap into your regular phone’s monthly allotment of minutes and text messages while communicating from home. There are other apps available for making free phone calls, but Viber has a reputation for providing the clearest audio of the bunch. Of course you can always install Viber on your activated smartphone as well and communicate for free anywhere that you have Wi-Fi or a cellular data connection available.
Viber is available as a free download for Android, and iOS.