If you use your phone abroad and turn data roaming ON using any GPS application may download small amounts of data when retrieving locations. For this reason we suggest the Data Roaming is set to OFF.
The settings we suggest are as follows:
iPhone Settings -> Mobile Data -> Data Roaming (OFF)
If you are on a fixed data plan or want to be extra careful about your data usage we also suggest turning OFF Cellular Data as well.
iPhone Settings -> Mobile Data -> Mobile Data (OFF)
Wifi should be left on for use where a wifi connection is available.
Note: Ski Tracks will not work in Airplane Mode.