Do I need to Jailbreak my iPhone in order to develop what I want?

[v2club]

I know that Apple wouldn't approve apps that change the behaviour of the OS but if I want to make such an app for my own use (and of course educational and testing purposes) can I do that without having my iPhone jailbroken (I'm ok with paying $99 and registering as a developer, that's fine as long as I can test whatever I want on my device...)?

 

[xArtx]

I know that Apple wouldn't approve apps that change the behaviour of the OS but if I want to make such an app for my own use (and of course educational and testing purposes) can I do that without having my iPhone jailbroken (I'm ok with paying $99 and registering as a developer, that's fine as long as I can test whatever I want on my device...)?

I sounds like a jailbreak app to me..
Anything that changes the Springboard and such is going to want to use MobileSubstrate, by Saurik for jailbroken devices.

 

[ChristianVirtual]

If you develop for yourself and don't want to submit to AppStore you can use also private API which might bring you further.
But you still be limited by sandboxing etc which will only go away with JB.
I might be wrong; as I never played with private APIs so not very sure whats "in" there.