Can iPhone | iOS4 run on the HTC EVO 4G?

It can be done, in theory, but it is illegal to do so.

iOS 4 is designed and complied to run on the iPhone hardware. the evo hardware is probably configured differently. if might be possible, but it would take some tweaking. but i doubt it

The iOS4 is Apple propriety software and can only run on iPhone and ipod touches.

Probably if you know what your doing and you can get the OS files and flash it onto the HTC's memory. I know that you can put Android onto the iPhone (with difficulty, and I don't know how..I read it on Wired.com) but I don't know about the other way round.

I highly doubt it. I find it interesting that you want to run iOS4 on the Evo hardware, because if it were up to me I'd like to run Android on the iPhone 4 hardware (except I'd like the larger screen of the Evo). Unfortunately, putting Android on the iPhone is technically possible (for the 3G I think, not for iPhone 4 yet), but it runs so poorly it's not worth it.

Not likely because you would need to fiddle around with the hardware for iOS4 to think it's running on an iPhone + you need to own an iPhone to 'own' a copy of iOS4.

no IOS4 the embedded OS for the new iphone was written to work on the particular chipset that apply build the iphone with and the iphone4 version of the ISO fully supports apple closed hardware.

if its was that easy we would not need Evo4, iphone4, htc etc brand it would be generic phone with your own os in it.