You will need to do a credit check, though I didn't have to do one there and then I don't believe, as their system was down, nothing was typed into a computer, except when I was paying. I just signed paperwork, paid and left.
You won't need your iPhone but you will need at least a credit or debit card. I think if you already have an iPhone you just swap SIM's, so you just get the phone.
Took about 25 minutes but 3 hours of queueing for me!