HWID = HardWare IDentification, which simply means what says literally. Units with the same HWID have identical hardware.

Don't try to flash any full Asian fw directly to your US device as you may well brick it. If you wish to try, use the original US boot.bin combined with the rest of the PH fw. Here isn't the place to tell you any more, but have a look at [Only registered and activated users can see links. ] and follow the first method substituting the fw and HWID as appropriate. You should also remove the US voice, keyboard & text files before flashing and afterwards replace them with the correct PH ones if the flash is successful, as the US files might cause a boot loop or boot freeze if they are different to the PH default files.
Don't ask further advice in this map thread though.