DDR3 ram works fine with AM3. It is just when RAM is labeled as triple channel you can't fully utilize it due to the lack microarch in the Phenom II processors.
they work excellent with dual channel memory
the i7s work better with triple channel memory since they can fully utilize it and that is why those setups are faster sometimes.
however, the difference is minimal you won't see the difference between dual channel and triple channel memory unless the computer is used for heavy calculations and simulations
you can't see it in gaming and multitasking
1333 and 1600 DDR3 RAM will work fine with the phenom II just remember to overclock the processor so that they synchronize