When using the Ribbit REST API there are many actions that can trigger REST events. Whether it is calling into your purpose number, receiving a new voicemail, or connecting another leg to an active call, REST will send an event to a URL you provide, called the Callback URL. Lets take a look at how to set up that Callback URL, and a basic way to inspect the data coming in the Callback Event in PHP.
You may have seen our Google Wave gadget that uses our Javascript library to create an outbound conference call to lots of people in a Google Wave. You really don't need to write a lot code to accomplish this.