Really? I don't need cellular signal?

Really. The current SkyShepherd collar doesn't even have cellular components. 

The exception is that, in order to create a boundary in the app, your mobile device will need connection to the internet to 1) load the map underlay (so you can see where to tap to create the points that define your boundary), 2) to search an address (if you need to), and 3) to save your boundary to your SkyShepherd account and list it in your boundary library.

After a boundary is listed in your boundary library, you can send it over Bluetooth to your collar without any internet connection. Your app sends the boundary to your collar automatically when you activate it. Your collar stores the boundary and uses GPS signals to contain your dog without any connectivity required.

Now, if you want to get collar position and status updates in a no-internet environment, you'll have to be close enough for Bluetooth connection, but at that point, you can probably see your dog visually. 

So, if you're planning a trip to No Man's Land, make sure to create the boundary you want to use there beforehand, while your mobile device still has an internet connection.