[broken link removed]
Comes down to how you use a phone and the size of the battery. I turn off bluetooth and don't use it as a MP3 or radio. I can get a week out of Sony w810i. Other phones with a good battery life seem to be the Sony K850i and the Sony C902. Nokias seem to be less good with battery life in general.
6300 760 mAh Li-Ion battery (BL-4C)
3.5 hours in talk mode and up to 330 hours in standby.
E51 - 1050 mAh, Li-Pol battery
4.23 hours of talk time and up to 13 days of standby
C902 930 mAh Li-Pol battery (BST-38).
400 hours in standby 9 hours of talk time
K850i BST-38 – 930 mAh Li-Pol unit (previously 950 mAh).
400 hours in standby and 9 hours of talk time.
W810i 900mAh Li-Pol battery is used.
370 hours standby mode and up to 8.4 hours of talk time
You'll get this info here...
http://www.mobile-review.com/review-en.shtml
3G uses more battery power than 2G.
iPhone 3G
Up to 5 hours on 3G Up to 10 hours on 2G
Standby time: Up to 300 hours