Both the iPhone and the Android apps can be used in places with no cellular connectivity as long as there is a GPS signal and as long as the phones are at least temporarily returned to a location with cell phone connectivity.
Geotagging of photos occurs via GPS regardless of cell phone connectivity and location information is stored along with the text and photo observations. When cell connectivity is re-established, uploads will occur and the correct geotags will be sent along with the observations.
If GPS is turned off, and there is no cellular connectivity to triangulate for secondary geolocation, then observations will not be located and location information will have to be inserted via the website for every observation.
The Android has an option to turn off automatic uploads in case connectivity is very slow or battery life is an issue. This option must be set back to “on” before uploads will occur.