According to the information had by Engadget the Dell Lightning is a Windows Phone 7 device. This will definitely occupy the high-end of the the line, as it has 3G, a 1GHz Snapdragon processor coupled with a 4.1-inch OLED touch screen. It also has a slide out QWERTY thumboard.
Next in the line-ups hierarchy is the Dell Thunder, an Android-based Smartphone with the same 3G capabilities, OLED screen and Snapdragon processor. It does away with the slide out keyboard though, but is as gorgeous (at least in the pics) as the Lightning. Aside from missing the keyboard, it also differentiates itself from the Lightning by bundling up apps for Facebook, Twitter, Hulu and Youtube in it's app arsenal.
The Dell Smoke is a bit of a departure, form-factor wise from the rest of the phones. It's candybar shape and QWERTY keypad reminds me of some earlier Sony-Ericsson Smartphone from years yonder. It has a 2.8 inch TFT screen, 3G and a 5MP camera. It also sets itself apart from the rest by having mutilple account support for Exchange and Active Sync, plus VPN support for secure connections. It has every indication, feature-wise, that is going to be positioned as a business phone.
The Dell Flash is supposed to be the 'mainstream' Smartphone of the line that will bring Smartphone goodness 'to the masses', meaning it will be cheaper than current Smartphones in the market offering the same function or feature set. Also Android-based, it will be powered by a 800MHz Qualcomm processor, come equipped with a 3.5-inch TFT screen, 3G connectivity, WiFi and a 5MP camera. The Flash is also being touted as having a better touchscreen keyboard better than what's currently available in Smartphones today.