Wikipedia
Voxer
Voxer is a San Francisco based mobile app development company most well known for its free Voxer Walkie Talkie app for smartphones.
Founded by Tom Katis and Matt Ranney, Voxer Walkie Talkie is both a live "push-to-talk" system and a voice messaging system. Messages on Voxer are delivered live as they’re being recorded and then delivered as a voice message as well. The app works on Android, Windows Phone and the iOS operating systems. In April 2012, the company raised $30 million in venture financing from Institutional Venture Partners (IVP), Intel Capital and other angel investors.