The price of the phone and the installment amounts are fixed at purchase. If there is a positive inflation rate you are guaranteed to make a real saving (but no

The price of the phone and the installment amounts are fixed at purchase. If there is a positive inflation rate you are guaranteed to make a real saving (but not a nominal one) by paying some of the purchase amount later on. What happens to your salary or the price of the phone later has nothing to do with it.