If they themselves quote a price for the iPhone starting from 650$, how is 99$ + 20$ a month for 20 months = 499$ dollars total full price? I'm still 150$ short

If they themselves quote a price for the iPhone starting from 650$, how is 99$ + 20$ a month for 20 months = 499$ dollars total full price? I'm still 150$ short and that's assuming a 0% interest rate.