Sorry to bump this, but I have to reant and change my opinion of Sony:
I have this phone:
http://www.sonyericsson.com/cws/corporate/products/phoneportfolio/specification/w595
I love it, it has tons of useful features and it looks much better than my old w810i. Only one issue with it, and it's a biggie- battery life.
It is quoted as having 15 days standby on 3g connectivity. I would not use the phone for calls, (less than 5 mins), sms, etc more ethan once a day, and I would only check its status (and thereofre activate the screen) once an hour. I'm getting 2 days or less out of the battery, and it seems to be getting worse.
The phone and the battery are only 2 months old, it's quite stupid.
My aunt and uncle have this same phone and they have the same problem. It's not a bad signal, we all have great coverage, bluetooth is always off on mine and i have followed every bloody suggestion sony ericcson has (all 3 of them) to no avail.
Even tried the old charging overnight trick (given it's a lithium-polymer battery, it's kinda redundant), no hope.
There has to be a dodgy set of batteries floating around or something- either that or sony can't make them. My old w810i's battery was loose, so every time i put the phone down too firmly on a hard surface or hit it a bit it turned off.
Sorry sony, but if you say 15 days, live up to it. I want a long-lasting 3G phone, so give me one or I'm defecting to an iPhone.