We RV travel a lot with another couple - each in their own RV.
For constant communication between the lead RV and the following RV, we use walkie-talkies that each of us leave turned ON all the time. The units have a power saver mode so their batteries last a long time - even when left on 24/7.
Pushing a walkie talkie button is way faster than using cell phones/smart phones .... and walkie talkies always work .... where cell phones/smart phones require a strong enough cell tower signal.
During our recent long trip that we just completed with another couple, they even used their walkie talkies between the husband and wife for backing up and positioning their travel trailer at campsites.
The good old walkie talkie is still alive and well.