I've created an app, that is self-explanatory. What is the etiquette in the iPhone world: do I still need to have an About button that explains what the app does, website, email, all that? Or is that unnecessary?
The etiquette in the iPhone world is to design sane applications. If your application does not need an About screen, don’t do it. Those who want support can always check out your application description in the App Store.
I wouldn't consider it necessary, but then again I would get a second opinion about your app being self-explanatory; you wrote it after all :) Seriously, I've found a lot of "obvious" UI and behavior I've written over the years to be not so, and it's helped to have opinions from others (especially those who don't use computers for day-to-day work) to bring more clarity.
But from an etiquette standpoint, I'd say no: in fact if your app truly is self-explanatory it'll just get in the way of what your app does, which is what consumers are after.
I don't entirely agree with zoul here. I think that every app should include information about how to contact the developer and/or get support if it's needed. Yes, you can put this information in the App Store listing, but that makes it more difficult for your customer. I'd say yes, add the About view.
I think that you almost always need one, especially in a paid application. You want it to be as easy as possible for your users to get in contact with you for support (no need to make an upset user angrier by making them search for your contact info), because happy users leave good reviews, and support requests often help you to figure out what needs work in your app. Additionally, if you release a free app but you also have some paid apps for sale, I think the free apps need an about screen that will send your users to your page on the App Store; after all, you might as well get some free, non-invasive promotion when giving away something.
The only time you probably don't want to include an about screen is when you don't want to hear from users. If you're giving away a free app, and you don't want to deal with people having problems with it, then don't even bother with an about box. Or if you're Apple, since about boxes in their apps would be redundant.