Lars, the scuttle I've gathered:
both are fun skis.
both can take alpine binders.
both are somewhat softer than their alpine brethren. I forget which B models they're equal to, but if you go to www.telemark-pyrenees.com
, you can find out.
I skied with a guy last Thurs who was on the SickBird with Fritschi Freeride AT binders. he raved about how fun the ski is.
I'm not happy with my AT skis (Black Diamond Havoc) and I'm considering selling them and one of my preferred choices is whatever "Bird" is the equivalent to the B3.
more info can be found on the TGR.com forums.