My darling sister gave me her old iphone 3. The problem: 24 hours of charging gave me about ten minutes use.
The repair took about an hour, possibly longer, including calling my wife to observe how scary it looked all in pieces. Those screws are impossibly tiny.
Take pictures at every step. Cable 3 would have given me heartburn on the reassembley if I had not taken a picture of how it looked before I pulled it out.
For every screw type I had labeled film canisters.
My magnifying glasses helped a lot.
For people who's phones are still under warranty perhaps you should offer a replacement "do not remove" sticker, as mine got all ripped up.