Vox me! http://goo.gl/X3dEi

Anyone can Vox you once they download the free Voxer app. Voxer is designed to be a Walkie Talkie application for smartphones. Features Include:

• Live Walkie Talkie
  Voice
  Text
  Location
  Photo Messaging
  Group Chats
  Offline Capabilities
  Playback Capabilities
  

Messages are streamed live and encrypted. Friends can participate live or listen to them later. The app is currently available for iPhone, iPod Touch, iPad, and Android devices.

The team behind Voxer was part of the team that developed the popular Danger Sidekick handheld device, as well as working with Apple, Google, and Samsung.

Of interest, Voxer just released Voxer Pro, a professional-grade communication system specially made for businesses. Perks include texting, photo, and location sharing, and "seamless" live audio and recorded message capabilities that mimic a walkie-talkie or 2-Way radio.

Voxer also recently announced that an app for Windows Phone is coming soon.