It’s been about 3 weeks since I recommended turning the 3G radio off in your iPhones to save battery life. In those three weeks I have enjoyed a very noticeable increase in time between charges. I can pretty much go through two days of normal cell-phone usage (that includes a lot of sms texting and e-mail usage, in my case) without needing to recharge.
I have also left the WiFi Radio on now constantly.. but I turned off the push service, that way I only get new e-mails and updates when I explicitly ask the phone to check for them.
I have not had the need to turn on 3G service in these last few weeks, it always amazes me how much WiFi coverage there is in El Salvador. It seems every restaurant, mall, hotel, and office has WiFi available for their customers.