An interesting graphic from David Isenberg shows how voice is already there on the Internet. The text accompanying the chart says that by 2006, 50% of voice calls will go over the Internet. That will only come true through user behavior changes if voice calls over the Internet become as easy, or easier, than picking up the phone and dialing. There are of course costs with traditional voice calls but I can't imagine that accounts for 50%, to the point of making users switch to something unfamiliar, daunting and less accessible than a phone with 12 buttons.

The other way for calls over the Internet to become easy is for the regular phone to remain our voice call appliance and to work the same way it does now, but for the phone companies to route over the Internet. I don't know as much about that business to know how it will work, but something tells me entrenched interests will resist that.