Hard to say but what I think this means is that you can take an existing AT&T SIM and use it in your iPhone without activateing the SIM via the iPhone.
Basically one step closer to a full unlock. I'm kinda surprised it has taken this long to get this far. I initially anticipated it would take a month to get to full unlock but I am surprised they haven;t gotten further along by now.
I have a cororate Cingular SIM paid for by my company that I have not been able to use since I got my iPhone, I've been forwarding that # to my iPhone # and paying the monthly 20$ data plan. I plan on giving this a shot later today, if my corporate SIM works in the phone for phone calls but no data, thats great but I'll be putting my iPhone sim back in. If this works for data and voice, I'm set.