I am still using a sixteen year old flip phone on a daily basis. The plan for it is as cheap as you will likely ever find. Most of my students cannot believe that it works until I show them. It is only used for phone calls, no texting as I just do not care to do that. There is a saying that goes: “Those who are naturally smart do not need a smartphone to think with.”. When I ask people hard questions, it is a bit sad to realize that many of them go directly to their phone rather that to try to think it out.