Can sprint tell if you bring in a different iPhone for your lease?

Can sprint tell if you bring in a different iPhone for your lease? - 1

Yes. They recorded the serial number when you bought it

Yes, every phone has a different serial number.

If you mean if the phone you leashed gets broken, can they tell if you try to turn in a different phone? Yes because the ESN will be different. Will they take the replacement phone, I suppose they would if it was the same model, memory, etc, but if you leased a 64GB phone and tried to turn in a 16GB or a different model number, they are going to make you pay the RETAIL difference between the two phones in THEIR favor. Which will more likely than not, be the price of the phones at the start of the lease.