Iridium constellation orbits at 780km, while Starlink is slightly lower at 550km. Don't know how much, if any, difference that makes in the signal strength requirements. As I understand it, Iridium was designed with the tradeoff of accepting weaker signals with lower throughput, while Starlink wants high throughput and needs a stronger signal.

Those are integrated into the iPhone 14. The throughput is so low that it's only for emergencies.

Significantly different use cases. Battery life, physical durability, etc are all significantly better than a phone.