Made for people who carry around two phones—one for work and one for your wife to nag you at work—this KTFT EV-K170 slider allows you to dial and receive calls with two numbers simultaneously. There are two modes, an "H" mode and a "B" mode (Home and Business, anyone?) that can be swapped back and forth depending on which number you don't want your mistress to see.
Other features: FM radio, 1.3-megapixel camera, voice recorder, and FM radio. It doesn't appear to be available anywhere outside of Korea—when's the last time you had a KTFT-brand phone—but it is a cool idea for cellphone cowboys.