Some Athlon II cpu's can be Phenom II based (they can just as easily be native Athlon II also, I guess it just depends on what AMD has on hand to make the model at the time). Its just a yield management exercise and a way to sell slightly "faulty" cpu's.
My cousin got really lucky with an Athlon X2 that he successfully unlocked into a Phenom II X4; he not only got the unlock, he got an easy overclock to 3.3 GHz with the stock cooler. It turned out SO nice that he upgraded his PoSU Coolmax "750" Watt (try *maybe* 400W
) to a Cooler Master Silent Power 600 W and his 9800Gx2 to a HD 4870-X2. And his CPU cooler is now a stock Phenom II X4 cooler with the heatpipes.
Phenominal (pun intended) bang for buck as a gaming PC; it is mostly for racing games and GRID looks and runs great on it .. So good,, i hear he now has a steering wheel and foot control (so much for "inexpensive upgrade", however)