Much like Nextel's Direct Connect from the late '90s, the App of the Day turns your smartphone into a walkie talkie. The app is called Voxerand has several different ways that you can communicate with your friends. You can talk to people instantly with the push of a button. Voxer also lets you send texts, picture messages, and show your friends your location via GPS. If you have Facebook, you can use the app to talk to anyone on your page.
Voxer is free to download and is available for iPhone and Android.