Making app for iPhone
It depends. If you have an Apple Developer account ($99 per year), you can create either a ad hoc distribution profile or use a development certificate. For more information on that, view here. Although it is called beta testing, it serves your purpose.

Now if you don't have an Apple Developer account, you can use jailbroken devices and Jailcoder. To use this method, follow the steps below:


Jailbreak your iDevices. If you don't know which ones to use, google it.
Make sure you have Xcode (Here if you don't have it)
Download Jailcoder from here.
Go through the "Guided Patch"
Now develop your program. YOU CANNOT RUN IT ON AN IDEVICE YET!
Open Jailcoder and drag-n-drop your .xcodeproj file into the box.
Connect the jailbroken iDevice and configure Xcode as you would if you had a legit developer account (https://developer.apple.com/library/ios/documentation/ToolsLanguages/Conceptual/Xcode_Overview/RunYourApp/RunYourApp.html)
Click run


An older video: http://www.youtube.com/watch?v=3NAm1MOGabw. Ignore the fact that it says Xcode 4. It works on Xcode 5.