There are 3 models shipping. They all have the same 4-inch screen and some controls along the side of that screen.
There are 3 capacities, 2GB, 4GB, and 8GB, and each capacity determines how many stations you can load onto the device. The stations are loaded via USB and they seem to load 100 songs from each station onto the device, obviously you can also connect live via WiFi.
The 2GB version sells for $200 and holds 15 stations worth of music and data with 500 extra megabytes for other music from your computer, the 4GB ups the station number to 25 with a full 1.5GB spare for personal media, it sells for $250. Finally, the 8GB version is the top of the line and sells for $300 and can load 40 stations worth of content with 4GB to spare for other music. There are still 2 different subscription levels though, the free one has the occasional ad and you only get 6 track skips per hour, the premium subscription does away with the ads, gives you unlimited skips, and even makes it so you can tag songs to play when you want them to, like they were in your own library.