I am interested in adding basic multitasking support to my iPhone app (i.e., fast app switcing), but also continue to support users on older iPhones and iPods who cannot install iOS4. Is there a good way to do this? I have heard that using respondsToSelector:, I can determine whether new methods are supported (and thus whether the user has multitasking support), but can I build my app so it can run on the older phones too? What is the best practice?