I remember the original iPhone well. I remember incredibly slow network connectivity but pretty darn good battery life. The iPhone 3G I replaced it with pretty evenly swapped those. I learned that it was worthwhile to turn 3G on when I really needed it and off when I didn’t. 3G giveth bandwidth and taketh away battery runtime.

My iPhone 4 today runs close to an entire day on a charge, which usually includes use for email, Twitter, Facebook, and Pandora. However, when I go to conferences, I find that the phone doesn’t last the entire day. Between more screen time, more Twitter synching, more email, it just tends to last about 75% or less of a day.

At a conference in October, I thought about this, and pondered something. Almost no apps on my phone actually need 3G all the time. In fact, most of them for background tasks (aside from Pandora) work fine with the older EDGE network. Apple has also been making WiFi connections a bit more promiscuous as well (such as WISPr for AT&T subscribers to connect to AT&T WiFi networks automatically, which likely results in battery savings as well when WiFi is available).

In order to improve battery life, when the iPhone isn’t in active use in the owner’s hands, Apple should run with slower (more power effient networks) such as AT&T’s EDGE as the default network connection if WiFi is not available and no app that requires background 3G (Pandora, Spotify, etc) or foreground 3G (Safari, Twitter, Facebook, YouTube, etc). In essence, when the phone is interactive, it still would run on a legacy network unless the app (as specified by the app developer at design time) pulled it to use the higher throughput network.

It may not prove viable on some networks if the carrier charges more for legacy network access than newer network connectivity. But where carriers do not charge a premium for legacy access, it could well provide a solution that would allow consumers to conserve battery life while making users do very little to get it.

The same could theoretically apply to 4G connections as well where devices or carriers would be using them – of course, Apple does not support any “4G” connectivity to date, but likely will in time when the market is there, costs are reasonable, and battery consumption is no longer abusive.