Apple today has updated its mobile carrier activation list by removing Sprint from the picture.

Customers who purchase an Apple Watch, cellular iPad, or iPhone will no longer have the option to activate Sprint. Also, all references to the mobile carrier brand have been removed from Apple’s online store. Prior to the move, Sprint customers were able to activate their devices and listed carrier deals.
The change should not affect too many people as Sprint and T-Mobile merged in 2020. A large percentage of Sprint customers have already been converted, although there are still some that haven’t transferred to T-Mobile. Sprint customers have used T-Mobile’s network while the latter incorporated the Sprint spectrum in April 2020.
Sprint customers who are experiencing problems connecting to the T-Mobile network while activating a device will have to call T-Mobile customer service. The T-Mobile rep will move their Sprint account to T-Mobile to resolve the issue.