just like what anyone uses their phone for... making calls installing applications, watching movies, using internet/movies youtube... ive installed many handy things.
but it does have a few downsides, like the bluetooth does not work, no flash you cant take video with the camera although there is a 3rd party application released that allows you to make videos ( not from apple )
also you must pay monthly for the iphone because they lock it so you can only use it with certain providers, unless you unlock it "illigally" with a program from the internet, but its still a very good phone not to mention 16GB space on my phone