The Payphone Project
github.com
github.com
If you can get your hands on (or build yourself) a red box [1], you could even hack your own hack.
I vividly remember the last time I used a payphone like this calling my then girlfriend (became fiance, became wife) outside a 7-11 in rural virginia before the turn of the century. Nostalgia by the bucketful.
He never fails to brighten the day of whomever greets him at the door at our house :)
I suspect the Payphone Project's mailbox locator was one of the first crowdsourcing web applications and predated the USPS effort.