Problem: My app must run on iPhone OS 3.0.

However, there are some features of iPhone OS 3.2 which I really want to use. Just as a little add-on for free. But I don't want to cut off my user base by doing this.

Imagine you're an iPhone OS 3.0 thing, and someone gives you a book to read. It has iPhone OS 3.2 instructions. You never learned those. So what do you do? Crash? They would have to be hidden, so you're not bothered.

Someone wrote recently on SO:

keep in mind that you have to check the version at places in the source code where you like to use the new features and provide alternatives for older os versions

So how could I do that? Wouldn't Xcode throw warnings when it finds stuff that isn't linkable from anything anywhere? Would I just check for the OS version and dynamically link - somehow - to whatever stuff I think is cool?