The issue isn't adding HD to a regular standard definition plan -- that can be done by anybody at any time. This topic is about people converting over to the Dish HD Only plans that only have network with high definition channels. They are at the top of the page here:
DISH Network - High-Definition and Standard-Definition Packages -1.888.825.2557
They are cheaper plans because you get fewer channels, however, for folks like myself it's a great deal because even with a lower channel count they still have all the networks I want to see in those packages.