Our system doesn't actually use the iPhone in order to geotag photos. Eye-Fi geotagging is based on the wi-fi networks that were in range of the card when the photos were shot, and when the images pass through the iPhone that does not affect the geotagging results.
In order for us to add geotags to your images if you transfer them to iOS, you must have another destination enabled, like an online sharing site (Flickr, Picasa, etc.) or Eye-Fi View, and after the photos reach the iPhone, and the iPhone connects to the internet, our app can automatically forward the photos to your other destination(s) and attempt to geotag them.
So if you're somewhere without data for the iPhone, the images can reach the iPhone, then they will stay queued up until the phone is back online, when they should forward and hopefully get tagged. Of course, if you're shooting in the middle of nowhere, there are probably no wi-fi signals around for the card to learn about, so I'm afraid they will probably not be tagged anyway. Here's some more detail about geotagging/WPS:http://support.eye.fi/software/problem/ ... eotagging/
I hope that helps.