If it not a BE(Black edition), you won't be able to overclock with the multiplier.
Lol... Noobs that can't read... He talked about ''Unlocking'' not ''Overclocking''...
And, YES a Phenom II X4 840T can be unlocked because the ''T'' at the end signifies that it is based on a Zozma Core (A Six-Core CPU with Two Cores Locked), With a ACC (Advanced Clock Calibration) compatible motherboard, you may be lucky and unlock two more cores! Or maybe just one or even if it is too unstable, you better re-disable them...