I was wondering if there was a way to connect the CrystalSky to a Cellular network when WiFi is not available.

I think Crystalsky works with USB 4G/LTE dongles. So yes you can connect Crystalsky to a Cellular network but you need to buy the USB dongle first from the network provider I guess.

CrystalSky is compatible with 4G dongles, we recommend MS-2131i-8（3G Global), 2372h-153(4G for Russia/Europe/Middle East/Africa) since these have been fully tested.

What is a 4G dongle and how do I download one

Info@DroneAds.biz Posted at 2018-2-26 05:08
What is a 4G dongle and how do I download one

USB device

Info@DroneAds.biz Posted at 2018-2-26 05:08
What is a 4G dongle and how do I download one

Don't waste your time getting a 4g dongle they are not supported by the CS, just hotspot the phone or get a myfi
https://forum.dji.com/thread-126259-1-1.html