After causing quite the fuss with its Deneb cores in Phenom II "X3 becomes an X4" models, we noticed the same trend with its entry-level processors, the venerable Athlon series.
German site Hardware-Infos posted a story detailing the unlock from Athlon II X3 405e into an "X4 B05e" processor. The CPU is relying on a processor core codenamed Rana, and we see that Rana is following Deneb's tracks. The difference between Rana and Deneb is just the presence of L3 cache. Deneb comes with 6MB of L3 cache, while Rana doesn't have L3 cache at all.
2.3 GHz Triple-Core CPU became a 2.3 GHz Quad-Core in the same way as Phenom II X3s became X4s. You need a motherboard with the SB750 Southbridge chip and turn on Advanced Clock Calibration in BIOS. After ACC feature is on, you should see four cores.
Ultimately, even if you don't acquire this platform, we cannot miss on an excellent, even though we believe unintended moves by AMD of late. We heard a lot of stories about Phenom II and how K10.5 came to life, but the core unlocking feature was an "innocent" by-product of flexibility in overclocking - after all, Phenom II are the first CPUs that go beyond LN2 cooling and can handle sub -200C temperatures. Core unlocking by Advanced Clock Calibration is a very interesting by-product of this newly found bond between the CPU and chipset, something we haven't witnessed in the past.
Now you know that Deneb was not the exception, rather the rule for X3-X4 unlocking possibility.