Just leave it on EDGE for SMS and voice and switch on 3G or LTE manually when you need to do something data-intensive. I get 2-3 days battery life this way.
Thanks, I shall give this a try, but I also play a lot of games and surf the internet on my phone, so that eats the battery like there is no tomorrow. Really, just stop making the phone so damn thin. It's thin enough, I need a bigger battery!