If I purchase an app for my iPhone can I download it for free on my iPad?
Yes. Purchases are tied to your iTunes Account, not to the device.
Yes, the app will be available for both if compatible. However, note that:
- classic iPhone apps don't look very well on the iPad
- "plus" applications look well on both the iPad and the iPhone
- HD applications only work on the iPad
So basically:
- some vendors are nice and provide "plus" apps that look good on both platforms (e.g. Smurfs' village)
- some other vendors are not so nice and force you to buy both the iPhone and iPad version (e.g. Angry Birds)