This is very much like the first century of clothing probably was. After technological innovation in the field ceases, you'll be able to use old stuff.
You can use a 50 year old wired POTS phone no problem. The sound quality is superior to modern wired phones, and those are superior to any cell or voip tech.
You can use a 20-, 30-, or 50-year-old scarf or jacket you find in a thrift store, but not a phone or a computer. And very few people would want to.