[aikinai]

Yes, the most common way to get jailbroken apps on your phone (Cydia) does not distribute pirated apps, but there is software that will allow you to sync pirated apps through iTunes.

I don't know the details of what you do to crack an .ipa (maybe they're not cracked and are just copied from a legitimate purchase?), but I know if you install something that blocks the iPhone's checks, you can install anything through iTunes.