I think it's been mentioned that the HG612 bitswaps more than the Billion 8800NL, so modems do seem to differ in this respect. I may have got this wrong, but I have a feeling that one difference between modems is how they deal with tones which have no bits allocated - some modems may mark them as permanently unusable (until there's a resync) whereas others will reallocate them. The HG612 is probably in the latter category.
