[Update: October 16, 2020: More Carriers Offer iPhone 12 $30 Discount]
It turns out that the U.S. price of the iPhone 12 and mini is $30 more if you’re not buying it through Verizon or AT&T. Those wanting to buy a T-Mobile, Sprint, or unlocked model are paying a higher price.
iPhone 12 $30 Cheaper on Verizon And AT&T
According to Apple, the mini starts at $699, with the iPhone 12 starting at $799. But that ‘starting’ price only applies to customers wanting a device on Verizon on AT&T. For those wanting a T-Mobile, Sprint, or sim-unlocked model, the starting prices go to $729 and $829. The price increase applies across the three tiers of storage capacity. As The Verge noted, there is no explicit reason given for the difference. Furthermore, it is not clear whether it is a temporary or permanent arrangement. However, the same price differential does not appear to apply for the iPhone 12 Pro or Pro Max.
But you can buy it directly from Apple at $699 why bother to buy from T-Mobile or Sprint at a higher price.