So weird, i HAVE 3G ON ALL DAY and use it for every streaming of music(sirius via music dock) or movies, all apps news, slingbox, etc., email, sms, NO PHONE CALLS,(calls all go to work Blackberry)and get thru the day just using the iP4 as a DATA device. On weekends with calls, #G time usually goes down. On work days, on 3G i average around 9hrs(useage), that gets me from 7am to 11pm every night
I've been amazed at the battery life of my new iP4. It's much better than my old 3Gs. I stay on 3G all the time and I'm never below 30% by 9pm. But I have great coverage with full bars all the time.
I've noticed when I've been on trips if I'm stuck working somewhere with poor coverage the battery life does decrease. I assume that the phone has to increase its power output to get good communication with the towers but that's just a guess.
I don't get more than 6 hours of usage on 3G, which is horrible. I mostly just send messages and check forums (like tapatalk) and that's fine for 2G. So I don't use 3G unless I'm going to update blogs with pictures, or email / instant message pictures. 2G on the other hand gives me around 10 hours of usage, which keeps me calm as I can go a full 24 hours of my life with the iphone without worrying. The other day I took it off the charger at 4 PM, and went to work, went out dancing, and stayed over at the hubbies and got home the next day at 3 PM, and I was at 56%, granted I didn't use it as much, but it was 24 hours with 50% left with a little use, like 4 hours. But there are times where I don't turn off the screen and I can go 2-3 hours and be at 75% or 70% battery life on 2G. I'd recommend 2G for using apps, or messaging. But for browsing, 3G. it's intolerable to browse on 2G. I wish Opera would do a better job with their browser. I used it for my BB and it was a lot better.