Doesn't work by default, but it can be done with iOS devices like iPhone or iPad (probably Android, too but I'm not familiar with it). Requires a small, simple hack.
The Phantom Wifi extender normally acts as a DHCP server and dynamically assigns your phone's IP address, Subnet Mask, Router/Gateway address, and DNS address when you connect.
When you connect to the Phantom wifi, look at these settings and write them down.
Now edit the Phantom wifi connection entry on your phone:
- change DHCP to Static
- enter the IP address you wrote down (192.168.1.215 in my case)
- enter the Subnet Mask you wrote down (255.255.255.0 in my case)
- leave Router/Gateway BLANK
- leave DNS BLANK
Now your phone knows the Internet cannot be reached on this wifi connection. So it will now use 3G/4G data whenever an internet connection is required. But it will still maintain the wifi connection as a local network, and the Vision App will keep working.
It seems to me that DJI *should* have programmed the Wifi Extender's DHCP server to always provide BLANK addresses for Router/Gateway and DNS in the first place. It's not like you can connect to the Internet thru your Phantom!
