Be very careful. I did try to SBF back to .602, and am getting the dreaded A5,70,70,00,1F MEM_MAP Blank error. If anyone is still on .621, has/hasn't rooted, and is handy with sbf_flash in Linux, I'd appreciate a PM to see if I can't fix this small problem. (and before you ask, tried the .602 and .340 SBFs. Both break, hard.)