This is super cheap. The iPhone 14 used to be my personal pick for the best unlocked iPhone deal but Apple has unfortunately discontinued that model now in favor of the latest iPhone 16e.

iOS 9.3.2, up to iOS 15.8.1 ...

Abstract: Presents corrections to the paper, (Corrections to “An Integrated Queuing Network Model for Optimizing Multi-Level AVS/RS Performance in Multi-Floor Manufacturing Environments”).