Voicethread: http://voicethread.com/
Browse these amazing audio blogs.
Here is a good example in using Voicethread
http://voicethread.com/#q.b577940.i3085807

The Flat Classroom Project, developed by Vicki Davis has fascinated and inspired me. It has continued since 2006. Davis's classroom broke down traditional walls, as students reached out to global partners in a collaborative journey of learning. Their project was named after and dedicated to Thomas Friedman's The World is Flat. An overview of this project and ideas on stretching one's digital classroom boundaries Navigate the Digital Waters can be found at http://preview.tinyurl.com/2vztth6