WiFi. That looks set to change when the rumored slimster -- codenamed "Shasta" -- launches in August. The screencap above displaying the results of an internal Amazon device query shows entries for "Shasta" and "Shasta WiFi." That would seem to indicate that Amazon's next reader will launch in two flavors: WiFi + 3G and 3G-only (our source isn't sure). There's even an outside chance that one could be a WiFi-only device. Another grab after the break.
Oh, and here's an interesting footnote: the original Kindle was apparently codenamed "Fiona" after Fiona Hackworth in Neal Stephenson's novel The Diamond Age. Many of the names in the device list above -- Nell (the protagonist), Miranda (mother figure to Nell), and Turing (i.e., Turing Machines) -- are all related to that very same story. What we can't figure out is how the word "Shasta" fits into all this so lay it on us Cyberpunks if you know.
Update: Freddo411 seems to have nailed it in the comments: Shasta, Lassen, and Mazama are all volcanoes in the Cascades.