The Free account helps you get to know VoiceThread. With 3 minutes of phone commenting, 5 VoiceThreads with up to 50 slides each, and unlimited voice and text comments, you can do a lot with a Free VoiceThread account! Take a look at this video to see the basic features of VoiceThread in action: Introduction to VoiceThread.
Keep in mind that you will not be able to share VoiceThreads securely or delete old VoiceThreads to make room for new ones with the Free account. You'll need to purchase an upgraded license to use those and other upgraded features.