Trade-in offers advertised as a large sum toward a new phone are rarely a payment. They are typically a stream of monthly credits attached to a service commitment.
The credit arrives over the device term
Rather than reducing the purchase price at the register, the carrier finances the device at full price and applies a credit to the bill each month across the installment term.
The full advertised value is realized only if the customer remains on the qualifying plan for the entire term, which is commonly two or three years.
Leaving early ends the credits while the remaining installment balance stays due, so the outstanding device balance becomes payable in full.
Plan requirements do the real work
The largest trade-in values are conditioned on a premium unlimited plan, and downgrading to a cheaper plan reduces or cancels the credit.
Because the offer is funded by the expected margin on that plan, the trade-in value effectively prepays a portion of service revenue the carrier anticipates receiving.
Comparing offers therefore means comparing total cost of plan plus device across the term, not the headline trade-in figure alone.
Device condition rules are separate
Advertised offers usually apply regardless of the trade device's condition within limits, but those limits still exclude devices that will not power on or have a locked account attached.
The traded phone is inspected after it is received, and a downgraded assessment reduces the credit, with the customer notified rather than asked.
Shipping the old device on time matters, since missing the return window voids the promotion even where everything else qualifies.
The carrier recovers value through refurbishment
Traded devices are graded, repaired where economic and resold through certified pre-owned channels, insurance replacement programs or bulk sale to processors.
Recovered value offsets part of the promotional cost, which is why offers are richest on recent models that hold resale value and thin on older ones.
Devices beyond economic repair go to materials recovery, where the value is in components and metals rather than in the working phone.
What the structure means in practice
A bill-credit promotion converts a device discount into a retention mechanism, since the cost of switching carriers rises with each month of unclaimed credits.
It also means the promotion's value depends on a household's own plan needs, which is a personal calculation rather than a property of the offer.
Reading the terms for the plan requirement, the term length and the early-termination consequence tells a customer more than any comparison of advertised trade-in amounts.