When you sign up, they run your credit. If they require a deposit, it ranges anywhere from $150-$750 depending on your credit. It's not as stringent as a bank loan or credit card and only you know your credit, and even though I worked for an AT&T indirect, I still have no clue what score equals what deposit. Anyway, the deposit has to be in cash. The deposit is in ADDITION to the cost of the iPhone. As long as you pay your bill, your deposit will be returned into 12 billing cycles(or close to a year). If you are late or have a non-pay suspension, your deposit is at risk. You can pay for the iPhone with check/credit card if you want to but the deposit definitely has to be in cash.