Quick question: Who exactly is iPhone Handoff for?

iPhone Handoff allows users to keep their number active on two iPhones, enabling seamless switching between the two devices. However, this feature is only available for users who have a new iPhone and a supported carrier plan. Apple's support website states that users can designate one phone as their primary device, while the other phone is considered a 'secondary' device. This setup allows users to keep their number active on both devices and make and receive calls and texts on either phone.