"According to a PDF document on AMD website, AMD processors which has built in memory controller, will support both DDR2 and DDR3.
In this document from AMD named "BIOS and Kernel Developer's Guide for AMD", Family 10h Processors, K10 Opteron/Phenom processor actually includes memory controller that supports both DDR2/DDR3. That is to say, if the board supports both DDR2 or DDR3 slot type (in future), a BIOS update will enable DDR3 support.
Looks like AMD is trying to play catch up with Intel P35 and X38 boards. We look forward to seeing new boards that supports both DDR memory types."