Designing phone ui for fingers first. While there were many other touch phones, many of which could be used with your finger(especially if you were a hipster, you could modify them to be more finger friendly), their ui was primarily designed for stylus use. This is a huge point that basically defined the OS and app design for the next 15 years.

Making capacitive screen popular. Before iphones, almost all(all?) phones had resistive touch screen, which required you to actually push your finger on the screen to do stuff. This was fine with stylus, less fine with finger. Capacitive worked with the lightest touch, which gave a smoother user experience.

Made multitouch mainstream and a core part of touch interface. Again, older touchscreen phones were mostly made to be used with a stylus, so multitouch wouldnt make much sense.

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It is important to note that one of the reasons apple succeeded was because nokia was too stubborn and late to adopt and promote touchscreen phones. Thats why while nokia was the phone bid dog of that day, users had turned to sony ericsson(SE) for their flagship, touchscreen phones.

And for 5 years before the iphone, people were using phones like the p800, that had a large touchscreen and even a removable keyboard for that full touchscreen experience. SE had taken nokia’s symbian OS and made it more touch friendly. Nokia continued releasing super capable(great cameras, video, fm radio, etc) but non touchscreen phones or with a small touchscreen for years after that, allowing SE to dominate that market. For example nokia released the 6600, which was a great phone but didnt have a touchscreen and its screen was small in comparison to SE’s touchscreen flagships.

The first iphone had a terrible camera and couldnt even film videos. Something that other “smart” phones could do for many years. The first iphone didnt have third party apps. Competitive smart phones had had apps for over a decade. The first iphone wasnt 3g, couldnt share stuff over bluetooth, etc. It was a pretty but pretty stupid phone in comparison to the competition.

But over time, apple kept improving, catching up and often surpassing competition in every aspect. I remember when iphones had shitty resolution and when apple caught up, they advertised it as retina display. Nowadays, iphones are the best or almost the best in everything. Now if only apple gave 120hz refresh on base iphones and a faster charging rate. And werent closed garden assholes.