Samsung patented a foldable smartphone with a spring-based hinge mechanism, check it out
This is no flip-phone, however, as there is a mesh-type textile sheet attached as the cover of an actual bending AMOLED display. The device is separated in two "bodies", connected via hinge portion. The hinge operates with a spring mechanism that looks incredibly old-school for a device that's supposed to be this hi-tech.
Samsung filed this patent application in the third quarter of 2014, which means this isn't a particularly recent development and could have advanced into a state where mass-manufacturing could be in consideration. That is, assuming Samsung actually kept working on it, rather than killing it to concentrate on the gazillion other projects it's running in-house. Still, the schematic does look very similar to the concept device Samsung had previously shown. It can be seen in the second slide.
Reportedly, a foldable Samsung smartphone, whatever its shape and form might be, is being tested with a configuration that includes a Snapdragon 620 or 820 SoC, 3GB of RAM, and a microSD card slot. It's supposed to be released sometime next year, given that Samsung expects to have production-ready foldable smartphones by 2016.