No such app. This means you have found either an app that needs to be made or there are reasons why there is no such app.

Because of the spammers this discussion will be moderated and link free.

-> Numbers such as Cell phone numbers are never free. At some point the app or company will need to generate revenue to pay for the numbers. Whatsapp doesn't use cell phone numbers so it's immune to that issue.

Google's system is currently subsidized by all that google is doing so it's not an example you can use to prove that phone numbers are "free".