We were just contacted by a representative from AT&T who saw our post about the leaked 4G policy memo, and wanted to clarify a very important point about their new 4G plans.  I quote:

Customers who currently have an unlimited plan can upgrade to a 4G device and keep their unlimited plans.

They did not dispute the validity of the leaked memo, but they were kind enough to tell us a part of the story that the original leak missed.  So put away those pitchforks.  Thanks for the clarification AT&T!