Some Premiere account have limits on what you are allowed to order. They have negotiated prices on specific phones. I'm assuming that in those cases, new phones have to be added.
So it may be up to your account admin or you rep to get the iPhone 4 added to your Premiere account before it will be visible as an option.
This is just an educated guess.
Edit: Everyone complaining that Premiere isn't answering....they aren't open yet.
You are correct. Premier accounts have the ability to tailor their offering. Your account admin has to add the iPhone 4 for you to see it.