Since this has been a topic of some interest at work, I thought I’d let you know how the battery life on the iPhone 3G is going. I have three email accounts set up: my personal IMAP, a .Mac MobileMe account, and my Amazon.com Exchange account, which is syncing email, calendar, and contacts. I turned off Bluetooth and WiFi: I use a wired headset for both phone calls and music, and I find 3G is quite fast enough for data. I turned off “push” email, and instead opted for “pull every 15 minutes” on all three accounts. I used it in this configuration all day, making several phone calls, checking email and calendar every 45-90 minutes, and reading my RSS feeds through Google Reader while riding the shuttle bus between Amazon buildings. After work, I took an hour-long walk, listening to The Maria Dimension by the Legendary Pink Dots. After all this (about 13 hours), the battery was about 60% charged.
That works for me.