I haven't heard of cell modems in particular, but I've used O.MG cables (described and sold here: https://shop.hak5.org/products/omg-cable https://shop.hak5.org

I haven't heard of cell modems in particular, but I've used O.MG cables (described and sold here: https://shop.hak5.org/products/omg-cable https://shop.hak5.org/products/omg-cable; I am unaffiliated with either Hak5 or the team behind O.MG cables) which can create an ad-hoc Wi-Fi network for management/C2 reasons. It's actually really easy to use (and almost scary, coming from never having used one of these). They are quite pricey, but way less so than older cables used by security and jailbreak researchers in years past, which would run into the five figures.