According to the tipster who leaked this information, the device will be available on Verizon and is going to be sold under the name the Samsung Continuum.
The info, provided exclusively to Engadget, shows that the secondary screen will be an OLED multimedia "ticker" of shorts. That is, it will be dedicated to displaying the user's most important information: news headlines, weather, date and time. It would assumedly be customizable.
As for the main display, it'll likely be a four-inch Super AMOLED screen. The device will probably pack in Samsung's typical slate of Galaxy S features, including at least a 1 GHz processor and 5-megapixel camera.
Additionally, the microSD card slot will be hot-swappable without the need to remove the battery. That's one of the most annoying things about Verizon phones, but this phone will change that.
Clearly, Samsung hasn't officially announced this yet but it does look credible.