after 1 unsucessful, and 1 semi successful attemt at this, here is how it goes on the 1st gen iphones.
the glass screen is fused(glued) to the back lcd and touch screen.
you can pry piece by piece by breaking the glass off chipping away at it as the glue is so strong u cannot remove in 1 piece.thhis procedure will take 1-3 hours.
once the glass is removed i ordered off ebay a new glass, turned out it was perspex not glass, stuck it on, firstly the touch thru the perspex is not as effective and the perspex scratches easily, also things like the light sensor that locks the screen when u hold it to your ear wont work as they painted the upper black section(instead of tinting)
on my second attemt at removing the glass from another phone i cracked the lcd.
ended up buying on ebay the lcd and bezel unit in 1 piece (about 100 bucks) and installed.
trust me, dont bother trying , was a waste of time in the end.
Hope this helps you as i know info on this is very hard to find, thanks.