How to use iPhone tracker on UK phone when in France

The iPhone must be connected to the internet via WiFi or the cellular data network in order to be located. If the iPhone does not have an internet connection, it cannot be located. Thus, unless constantly connected to WiFi, you'll be using cellular data-expensive in a roaming situation. Hard to believe O2 can't give you a straight answer regarding this.

The problem you're gonna face with the original iPhone is the fact that, by design, it is meant to ALWAYS have a data connection. iOS 4.0 introduced the ability to turn cellular data off in settings, however iOS 4.0 is not available for the original iPhone. iOS 3.1.3 is the end of the line for that model, thus there is no way to completely turn cellular data off on that phone. About the best you can do to minimize data usage is make sure push & fetch are off(no longer required for the Find My Phone feature), only check email when connected to WiFi or use apps that require internet access when connected to WiFi. However, I suspect your data usage will still be high/expensive. I did mention that roaming was extremely expensive, didn't I?