Hi
3 ways of doing it...
1) You can get a lead which goes in the iPod connector at the bottom which splits out to 1x composite phono plug (yellow) and 2x L/R audio phone plug (red/white) which you could use to play video on the TV and plug the audio in the TV or hi-fi speakers.
2) A 3.5mm jack to 2x phono lead which you can use to play the audio feed of your iPod into your hi-fi etc.
3) If you have computer speakers which have an inbuilt amp (so they'll be relatively good quality) and it has a 3.5mm jack lead to plug into the computer, then you can use the same lead to plug into the iPod as they have the same size connectors.
Not sure about how to plug it into a PS3 as I don't have one. Does it even have an aux in or similar to able to plug anything else into it?
EDIT!!! Now I have typed this all out, I realise you mean iPhone and not iPod - you should be able to do exactly the same with the iPhone, except you may need an adaptor lead if you plug anything into the headphone socket as it recessed on the iPhone. You can get one of these from eBay.
HTH.