How is this different from iMessage? You can simply raise your phone to record an audio message and same to play back a received one and they only last 2 minutes after being played (with the option to keep them manually).
With iMessage, you have to raise to ear twice: first to listen, then to record a reply. And then you need to tap a button to send it. With Overtalk, all of this is done in a single raise-to-ear session.
Thanks for the clarification, it makes sense now. While I wouldn’t personally use this (not a fan of voice messages to begin with, as I’m always in an office environment where people can hear everything) I wish you the best of luck with your project!