People used the web in radically different ways after a critical mass of people shifted to unlimited plans.

The same could be true of cell phones– unlimited voice plans could enable valuable new voice services that were previously infeasible.

For example, imagine being able to use your car speakerphone to play any audiobook you wanted, on demand.

All the technology has been in place for years– somebody just needs to license all the audiobook content, add a voice recognition interface for selecting the content I want to hear, figure out a pricing model (a la Netflix), and market it.

The only thing that has changed is that now, for $99, I can listen as long as I want. (The carrier might hate it, but it’s certainly compelling to me as a user!)

This is just one fairly obvious example of the sorts of services enabled by the new economics; there will hopefully be a flood of innovation in this direction.