I think the points here are:
- It's good to know that this is possible.
- It's good to know what your mobile plan includes.
- Even a cheap mobile plan will cover a few gigabytes of data. The route file for the complete Trans Am route, with cues, clocks in at about 3 megabytes, or 0.3% of a gigabyte. Downloading a route file isn't going to put you into overages (or if it does, something else would anyhow).