Woman and guys with belt-holsters had it right—it's better to keep your phone away from your body.
The NYT quotes the editor of Battery University as saying mobile phone batteries last longer if they're kept cooler. Cooler, as in not at your body temperature. So, if you're really running low on juice during the day, get a holster or a purse. Plus, you should probably keep your junk cool and away from your mobile phone if you ever want to have kids either. It's win/win.
There are other tips such as shoving a wet phone in rice, putting a car alarm fob up to your chin and freezing a broken hard drive we've seen before, but head on over if you need a refresher. [NYT]