Mumble

Mumble - High quality, low latency voice chat
Mumble is a free group voice chat application. It allows you to talk to your friends on the go, and has finally arrived on the iOS platform. Simply find a public server and join it to chat with your friends!
Mumble requires a connection to a server to function. Servers can be rented from commercial hosting companies. The Mumble server software is also available free-of-charge under and open source license, so individuals are free to create their own servers, without limitations. See https://www.mumble.info for more information regarding Mumble servers.
Mumble provides the following features:
• High quality, low latency voice chats via WiFi or 3G using state of the art codecs
• Access to thousands of public servers -- free for you to use when chatting with friends
• Ability to chat with hundreds of thousands of regular users of Mumble around the world
• An easily accessible list of all of your favorite servers
• Connect to and list available Mumble servers on the local network
• SSL/TLS encryption of connections to remote servers; voice data encrypted using OCB2-AES128
• Strong and flexible authentication with remote servers using either passwords or X.509 certificates
• Advanced audio configuration, allowing users to configure the quality and bandwidth
requirements of their transmitted audio (perfect for 3G connections with slow upload)
• Push-to-Talk and Voice Activated audio transmission modes (for hands-free operation)
• Flexible user-to-user and user-to-channel text messaging system for sharing links or images while talking
• Basic user functionality on Mumble servers (server administration not possible)
• Push-to-talk transmission mode.
• Echo cancellation for the built-in microphone.
• Bluetooth headset support.
Mumble is open source software, developed collaboratively on the Internet. Mumble and its server software are available for free, for anyone to use. For more information about Mumble, please visit our website at http://www.mumbleapp.com.