How is PuchiDen different from WhatsApp or Skype?

WhatsApp, Signal, LINE, and most messaging apps only reach other users of the same app — useless when you need to call a bank, a hospital, an embassy, a hotel, or any government office.

PuchiDen reaches any phone number on the public telephone network, and the person you call does not need to install or sign up for anything.

Skype works similarly but requires you to install an app on your phone, which means you'll need to have a workable smartphone to use, and Skype doesn't exist anymore.