I have several phones for the sake of testing website design responsiveness but I use the new iPhone 5 as my main phone. iOS is a great system to have for my phone simply because there's a huge library of good apps available for it along with good indie developers that supports them. The user interface of most apps is nothing short of amazing, too.
I've been using an iPhone for many years and the iOS along with the OS X for Mac are some of the few reasons why I even started learning Objective-C many years ago. Now I'm making my own apps written in Objective-C, but still continuing to learn the said language for the most part. You just can't learn everything in just a few years. I'm just currently working alongside other developers with their apps. If it's not the UI, it's with the core functionality. I don't have enough dedication to support my own apps just yet.