I guess if you want to do hardware hacking, you'll always be voiding your warranty. I don't see how you'd have to void it to use an iPhone how you see fit.
I run whatever software I want on mine, open source stuff, stuff that's never seen the appstore... and that's without jailbreaking it.
As I understand it, on android, you'd have to jailbreak it.
If the complaint is that apple doesn't allow malware on the AppStore, I think that's a good thing. Its not like Apple only allows software Apple thinks is good on the store. (though I do wish they would be more restrictive in that regard.)
Always I see the claim that android is "open" or the assertion that the iPhone causes a "lack of freedom".... but rarely are there any specifics. This forces me to guess what you're talking about in order to argue a different point. You're now in a position to say that all of my examples were not what you were talking about... which is the rhetorical value of vague complaints.