VoiceThread is a web-based application that allows you to have an asynchronous conversations and to make comments using any mix of text, a microphone, a web cam, or uploaded audio file. VoiceThread runs inside your web browser, so there is no software to download, install, or update.
Here is a tutorial that explains how to create a free VoiceThread account
Here is a tutorial that explains how to change your VoiceThread notification settings.
Here is a turorial that explains how to change your thumbnail image.