iOS 27 adds a feature on Monday that lets your same phone number ring on two iPhones at once; on T-Mobile, it costs $5 a month, which is probably an easy yes for dual-phone households. Additional carriers are supposedly coming soon. This is quite an interesting feature. I get having two lines via eSIMs on a single smartphone (e.g., one for personal and one for business), but this is a different approach.
If you have an iPhone Duo and an iPhone, they make a great pairing. Being able to hand off a call between these devices makes work pretty seamless. That being said, I think it may be a niche use case. And, of course, there is the additional monthly fee. While $5 isn’t a lot (especially if you can afford a Duo or new-ish iPhones), it will add up. This may be more for business users. I don’t quite see the family use case yet.
If you want to learn more about this feature, check out MacRumor’s write-up, which breaks it down pretty clearly.