Skimming through the article, I think it does not include cost of labor. In a developed country, my guess is that the cost to have a human worker collect, clean, setup, connect, etc. all the 84 phones would be actually higher than buying a new server.
In third world countries, this could be a different story. I would be happy to send my old phones to Africa to be used at schools.
In third world countries, this could be a different story. I would be happy to send my old phones to Africa to be used at schools.