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The best way to ensure the signal doesn't degrade is to make the phone bigger, big enough to put in a 4' or 4.3 inch screen, and while doing so, putting the antenna back inside the phone. :D
 
A touch screen rear back plate could be quite useful.

Would explain the bumper case as well.
 
iPhone 4S, built in Bumper. ;)


To be serious though, keep the screen at or under 4". Anything bigger and I don't know if I'd buy it.
 
Bigger screen. Faster processor that can handle real multitasking, not the fake multitasking they're doing now. More memory- you allow for HD recording and the largest drive is 32 gig? Wow. A way to add buttons - the iphone will never compete with Nintendo for serious gamers without buttons. And to those saying Apple isn't competing with Nintendo...oh yes they most definitely are.

No for gods sake. no real multitasking. i actually love what they have done there. thou they could have added a few more multitask api:s
 
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