There’s a NDA you get to sign when you sign up to become an apple iphone developer. Since I didn’t, I’m breaking nothing.
You are disallowed from writing apps for jailbroken iPhones when you pay the $99 fee. That’s why people who are working on official apps are unable to port them to the jailbroken Installer.app ‘free app store’. Pretty lame of Apple, huh? It’s like forbidding people from creating apps that work on 10.4.