Down payment ??

Depends on where and how you buy it.

If you buy it from Apple directly under the iPhone Upgrade Program, there is no down payment. The cellular service plan is not included in those payments. You need to contact your carrier to set up or transfer your plan if you already have one.

See here: iPhone Upgrade Program - Apple

If you are buying it in some other way, you'll need to explain what that is for more specific answers.

Note that all Apple finance options, including the iPhone Upgrade program actually involve you qualifying for a loan from their finance partner. For the Upgrade program in the USA, that is Citizen Bank, and for their normal finance purchase option it is Barclay Bank.

So you must qualify via a credit check with those financial companies, they effectively pay Apple in full at the time of purchase, and you enter into a payment agreement with the finance partner.

Apple itself does not provide the financing - you are taking out a personal loan with a bank who has partnered with Apple to offer the finance packages.

So be sure to read the terms and understand what you’re committing to. For the upgrade program see

iPhone Upgrade Program Terms and Conditions

And for the normal finance (of any Apple product) from Barclay see

Terms & Conditions. (while it’s 0% as long as you pay in full within the term period, note that the interest rates if you don’t may be very high)

Ways to Buy an iPhone - Apple