It is not exactly a secret that Phenom Triple core processors in fact are a quad-core processor with one core disabled.  Now before we begin out little tail and you storm off to the stores, realize this .. one core being disabled is always for a reason. It might be a problematic core, slightly instable or just downright damaged. But if you are in luck, the 4th core works properly.  And now let me continue my little tail ..

A Korean user has discovered that it is rather easy to unlock the disabled core on Phenom II X3 processors, provided the motherboard supports the Advanced Clock Calibration (ACC) feature (790GX motherboards) and this trick seems to work with Triple core Phenom II X3 720 and Phenom II X3 710, codename Heka.

Only with the 904xxxx-stepping; this tweak seems to work, not with 0849xxxx. On an ASUS motherboard this little trick did not work, but it's confirmed to work on 790 motherboards from Biostar and Asrock.

In this example a Phenom II X3 710 was paired with a Biostar TA790GX 128M motherboard. The CPU was overclocked to 3.12 GHz, with a vCore setting of 1.37 V.

Here's what you could try out:

Set the appropriate BIOS setting for the Advanced Clock Calibration feature to "Auto", save settings and restart. The system will be able to deal with the disabled core, and off load some work to it. The processor with the "additional" core was tested to be Prime95 stable and was able to boost 3DMark06 CPU score by as much as 1,000 points. More screenshots here.

For those interested, the Phenom II X3 720 2.8GHz sells here for $149.99