Originally Posted by
gfunkdave
It's probably not explicitly allowed but won't harm anything either. It probably won't work, in any case. The GPS chip in most phones needs a cell signal to give it its initial rough location before it can fine tune things.
The GPS works fine without cell signal, but the phone may not be able to late you on a map without a data signal to download the map. There are offline map products, though.
I'd think that you might need to hold your phone up to the window to get a solid GPS lock, though, and that may raise some eyebrows.