ReadWriteWeb published a guide that explains one of the easiest ways how disloyal Steve Jobs followers can install "Frash" on their iPhone. This application is an alpha port of Flash 10.1, it's developed by the same hacker that created the Spirit jailbreak and the JailbreakMe.com website.
To install Frash properly, you'll need to refer to a how-to guide, like this one hosted on Redmond Pie. But to sum up: You must first jailbreak your phone, download the .deb, upload it to a folder on your iPhone using SSH, restart your phone and... what's that? Did I lose you?
If all that sounds too hard, too geeky or too time-consuming, there is another way, as I discovered this morning. You can just install Frash from Cydia, the jailbreak app store instead.
In order to accomplish this feat, you'll need to already have a jailbroken phone.