To put an HTC theme on an iPhone 4 you will have to jailbreak your phone and use appropriate software to download the theme.
To put a theme on an iPod Touch, you have to jailbreak the iPod Touch.It depends on how long the song is, and how many MB or GB space your iPod has.
Amazing Grace
Amazing Dance Music!
Red Remix by Toxic
No, most jailbreak tools are free, however most good apps even on jailbreak app sites cost money. You can't use iTunes gift cards on these, but you can on the app store.
You cannot get a picture behind your apps on the iPod Touch through regular settings. You have to jailbreak your iPod Touch and download a theme to get that theme behind your apps.
ether amazing red or crimson
Amazing by Kanye West
the united kingdom
If you update your iPhone/iPod, you will remove the jailbreak, then you would have to wait until the jailbreaking websites invent a jailbreak for the new ios, but why update if you jailbroke it?
You can re-jailbreak your iPod Touch if there is a jailbreak software for your newly updated iOS. Chances are if you updated to the most recent firmware, you will have to wait awhile before a jailbreak comes out for it