Take this with a grain of salt, until more tests come in. WirelessInfo, the site that does 15,000 word cellphone reviews just finished testing the iPhone's battery life while talking and browsing, and it's not looking even close to the rated specs, or the other phones in that battery life chart that Apple published. 4 hours and 3 minutes of voice, and 3 hours and 11 minutes using the browser and EDGE; if they'd gone for 3G, that would even be shorter.
The thing that takes a lot of power is that giant screen. This conflicts with a report from Engadget that battery life was better than expected. My own experience has been mixed, but I haven't tested rigorously enough to make a statement. Talk time was originally rated by Apple at 8 hours, and 6 hours of Internet use by Wi-Fi. The discrepancy for browsing could come from a darkened backlight, and use of Wi-Fi instead of EDGE, but who knows why the talk time is bad. And why didn't anyone in the first round of reviews catch this? We'll have to wait for a second confirmation of this before we declare this the truth. Wireless info dudes are doing more testing as we speak. Stay tuned.
Update: The guys over at WirelessInfo have finished another round of talk testing using a different iPhone under the same conditions, and this time came up with 5 hours and 1 minute—almost an hour longer than before. So what was the deal? Bad battery? Bad charger? WirelessInfo doesn't know, but they aim to find out. They are currently running similar tests on the four iPhones in their possession. [Wireless Info]