Can anybody help to identify this app?

Hi, sorry if it's in the wrong place and sorry for my bad English too
My friend told me there is an app, you can talk with people by voice. They don't see you, you don't see them, they don't know your number, you don't know their number, you just talk with them with only voice, like when you call someone. And the app is accessible.
We both don't know the name, can anyone help?
I want to find it so I can improve my english and spanish by speaking

Forum: 

Vorail or Threema, perhaps?

Sounds like either Vorail or Threema. Both of these apps allow you to talk with other people using only your voice. Good luck finding the correct app if neither of these are it.

Thank you

Hi, I downloaded vorail but I don't want to use Icloud drive, what should I do?