Although leaving my iPhone 2g on the lawn to get soaked by the sprinklers was a good excuse to upgrade, I've never had the heart to actually throw the broken thing away. I finally decided I might as well try to crack it open so I ordered tools and a replacement battery.
Opening the phone was easier than I expected. All told, I spent about an hour opening the phone, desoldering the old battery, soldering in the new one, and cleaning out some lint with a dental pick and canned air. The phone looks almost as good as new now, although some of the seams aren't quite as tight as they were from factory. Now I want to try repairing all my busted down gadgets.
I cut my fingers a few times on the sharp edges of the aluminum iPhone back, so be careful! Also, use some desolder braid to clean up the pads where the battery is soldered in.