Glass back? Maybe. But just can't imagine they'll back down on user-replaceable batteries.
Daring Fireball Linked List: 2006 Apple Patent for Ceramic Enclosures
Maybe? Naaaahhhh.
iPhone 4G: is this it? -- Engadget
Although, if actually real, imagine how much fun the Apple engineer had sobering up and realizing he'd lost it in some shitty bar.