One very strong contender in this sector is Voxer. Voxer is an iphone application that gives your phone that Nextel push-to-talk functionality. With this beauty installed, you’ll be rocking your iphone like a walkie talkie on steroids.
Within this app, you can share voice messages. You can also send pictures, location info and text-based chat messages. It’s really a total package that pushes just about everything you can imagine back and forth to your fellow Voxers.
Of course, the real benefit is that you’re not using voice minutes or text messages to do all this cool stuff. That means you’ll save money. The app works over your wifi or carrier data network. It even allows you to record messages when your offline and it will automatically send them when you back online.
You can check out Voxer in the App Store.