What about other computing questions, about things such as PDAs? I guess this is kind of related to Are iPhone, iPod, iPod touch questions computer related (SuperUser)?
SuperUser is for generally all consumer computing questions. This can involve computer hardware such as everything in the actual computer casing, to monitors, printers, routers, etc. etc. etc.
Smartphones such as the iPhone and blackberry are also legitimate questions. iPod Touch is generally accepted since it is using the same OS as the iPhone. Other iPod and mp3 player questions generally must have some form of computer interaction involved for it to be legitimate.
Unless your peripheral device hooks up to the computer, then it will most likely be closed as not a computer question.
So even if the iPhone or PDA has computing parts and guts, it's not considered appropriate/related for SU unless you have it interacting with the computer.