What type of apps are you looking for?
You can allocate different ringtones to people that are calling you if they are in your Contacts app. Go to Contacts, choose your person and touch Edit on their page, scroll down to Ringtone, which will say Default, press the arrow and choose your ringtone for that person
No, I mean you know how you ring someone and you listen to their phone ringing don your phone until they pick up (same as you use an ordinary telephone), i want to customize that sound into music.There is a name for it but I dont know what it is ! I heard you can customise it so that a person can a pice of music rather then the standard tone.
You can't change the calling ringtone, it's transmitted by the network (O2, Vodafone etc.)
There are nearly 500,000 apps for the iPhone, if you can tell us what you want to do on the iPhone, then we may be able to help