I WILL keep the 3G always switched ON.
Also continuous syncing of some services like Gmail, Twitter, Contacts/Calendar/Task apps, WhatsApp, FlipBoard/GoogleCurrents, SimpleNote, Instagram, IM, RescueTime, some SMS sync app, etc.
I am not a heavy music listener: at max 1-2 hours a day but most probably on Bluetooth so let's add 1-2 hrs BT. Music listening shall not be over Internet but local.
I will take hardly a few pics a day - 5-10 maybe. Most of the days less/none.
No video recording.
Video watching on YouTube (or Video etc) will be maximum 20-30 mins.
No game play.
I will use it over GSM. 30-60 mins talk per day (approx). Almost never a video call.
I am currently on Galaxy Nexus which is an awesome phone (esp. without Samsung s/w crap) except for it's sucker of a battery. It doesn't even see me through 12 hours or full office (9-10) hours. So, I am planning to switch to iPhone and also because I want to get into iOS dev.
What about heating and crashes etc?
That's pretty much it. So, how much do you think a full charge should last. I do not plan to carry around a spare battery or even a charger. Well, I might have a charger but let's say I do not.