iPhone battery replacement surgery - almost a success...
20 - 30 minutos
My iPhone 3GS is about three years old and the battery was lasting only a few hours at a charge.
It went okay, but there were bad consequences, namely my vibrate stopped working. I don't know how I could've damaged that, but I did.
But other than that, the iPhone works wonders and the battery lasts for a long time now!
The ifixit guide isn't detailed enough and there are some vague tips, like "use the spudger to disconnect the ribbon from the left side" which when you've never seen a ribbon that tiny, doesn't help much. I had to use videos on YouTube to complement.
DO NOT try to pry open the silver rim, this is not an iPod. I tried that for almost ten minutes and it might be why my vibrate got damaged. The screen is like a lid and comes right off. Also make sure you put the suction cup near the home key.