The deposit is directly reflective of how bad the credit is. If you have a couple of minor hits, it will probably be around $100; if you have a bunch of bad stuff, it could be upwards of $500.
It all depends.
Yes, the first iPhone had a credit check as well. You could do it in the store before you bought the phone and they would give you a number to enter into iTunes when you activated. Your other option was to take the phone home and leave it up to chance whether you would have to pay a deposit or not and do the credit check through iTunes.