They... would do absolutely nothing, and so I don't think that you can...
One reason I oppose jailbreaking is because of the useless and pointless gunk that people put there just for show. Some stuff like PDAnet or Netshare actually have uses, but putting icons there (and spending all that time in the process) just for looks is dumb and pointless.
did the OP ask for your opinion?
I have an idea. When you install a theme. SSH into the ipod and go into the themes folder and rename the phone png to any other app name you like. That app will have the iphone icon.
Why would you want your iPod to look like an iPhone? That would be pointless... not to mention... a lie.