From Friday's HN post "Confessions of an Apple Store Employee":

  "We usually have to tell them that if they unlock their iPhone, it won't work. That 
  it's going to be like a $700 paperweight, and that the antenna will fry itself 
  on T-Mobile. Of course, that's not true, but that's what we tell them."

Wonder how quickly their tune on that last part will change..