“We wanted the best web browser in the world on our phone, not a baby web browser or a WAP browser, a real Web browser, and we picked the best one in the world, Safari, and we have Safari running on iPhone. It is the first fully usable HTML browser on a phone." (Steve Jobs, Macworld Conference and Expo, January 2007).
It's unclear whether Safari is the best browser in the world or whether iPhone has the first usable mobile phone browser, but one thing is for sure: many web sites launch iPhone-optimized versions. Maybe it's cool to have a website that looks really well in iPhone or maybe it's fairly easy to target a single mobile phone, because I've never heard about a website that launched an interface optimized for Opera Mini or Nokia's S60 browser.
Google Calendar released an interface for iPhone, based on the mobile version launched in May. Each calendar has a distinctive color, so it's easier to locate important events. Google Calendar for iPhone is available at calendar.google.com, but you can also try it at TestiPhone.com.