I bought a $5 galaxy s5 at a garage sale. I did not activate it, so it costs me $0 per month. I use it as a tablet, connect to wifi and use apps. I have a turn by turn navigation system (Osmand) that works offline, when there is no wifi. I use google hangouts-dialer-voice and can make calls/texts when I have wifi, callers can leave me messages and texts when I don't have wifi. I have a lot of music on my 128 Gb SD card, so my phone is my sound system, either with headphones or a bluetooth speaker. I also have a large library of pdf books on the SD card, mainly for reference use because I prefer to read paper books. I have a few offline games to play. My phone is my camera and video camera, and I can do basic video editing. With wifi, I can do the usual web surfing. I have apps that show me where there are campsites, rv dumps and water sources, whether I am offline or on wifi.
A smartphone is a very useful device which costs nothing to operate if you don't activate it and you use free wifi.