I have 2 phones, both exactly the same.  One was damaged and insurance co. replaced it.  Old one still works (just some cracks on the back).  Of course, I switched to the new phone with my carrier and it works fine with my mavic mini.  The "old" phone was then "deactivated".    All the apps are still there and it updates fine via my home wifi.
Now, can I use the "old" phone with the mini inasmuch as it has no data plan?  I can get internet if I am close to a wifi source.  
I'm thinking that the phone uses the phone company 4G data to make the GPS more accurate but I don't know if the mini uses that or if all the GPS just comes via the drone and the controller.
Anyone know?
Thanks!

Now, can I use the "old" phone with the mini inasmuch as it has no data plan?
Of course you can.
The drone doesn't need internet data to fly.
Lots of flyers (including me) fly with wifi only tablets.

I'm thinking that the phone uses the phone company 4G data to make the GPS more accurate but I don't know if the mini uses that or if all the GPS just comes via the drone and the controller.
Data isn't going to make GPS any more accurate.
Your drone has a perfectly good GPS receiver that it uses for all flight functions.
It's where the drone is that matters .. not where the phone is.

Labroides Posted at 8-13 05:45
Now, can I use the "old" phone with the mini inasmuch as it has no data plan?
Of course you can.
The drone doesn't need internet data to fly.

Labroides:  Thanks.  That's great.

Labroides is spot on. Just like him my iPad is wifi only, been flying that way since I started.

The flight control in DJI Fly should work fine. The only things that might not work without cellular Internet are the map and the flight authorization.

The in-app map could be worked around by "pre-cacheing"... while connected to WiFi, open DJI Fly, open the map, and scroll to the area where you will be flying. it should keep that area in memory.

If you will be in a DJI Geo Zone, you probably could get the authorization while on WiFi as well, before heading to the flight area.

Mind you, I haven't tried this myself.

Hello there archer180. Thank you for reaching out and for the information you have shared with us.In addition to this post, you will be needing an internet when updating your DJI Fly application. It is recommended to put your mobile device on airplane mode while flying it would lessen the interference like receiving calls and text messages while on flight. In addition it is not necessary to put your device in airplane mode but please make sure there is no such calls/text message or any notification that will interrupt you when using your device while flying your DJI Drone. Thank you and have a safe flight always.

DJI Stephen Posted at 8-13 20:42
Hello there archer180. Thank you for reaching out and for the information you have shared with us.In addition to this post, you will be needing an internet when updating your DJI Fly application. It is recommended to put your mobile device on airplane mode while flying it would lessen the interference like receiving calls and text messages while on flight. In addition it is not necessary to put your device in airplane mode but please make sure there is no such calls/text message or any notification that will interrupt you when using your device while flying your DJI Drone. Thank you and have a safe flight always.

Good idea DJI Stephen.

Labroides Posted at 8-13 05:45
Now, can I use the "old" phone with the mini inasmuch as it has no data plan?
Of course you can.
The drone doesn't need internet data to fly.

Yo, you need GPS data on phone if you want to make follow me with Litchi

djiuser_RIeSM3mAo5mf Posted at 8-14 02:57
Yo, you need GPS data on phone if you want to make follow me with Litchi

you need GPS data on phone if you want to make follow me with Litchi
Yes... but that has nothing at all to do with internet data.
GPS data comes from satellites in the sky, not from the internet.

Labroide I refer about Airplane mode ON which Stephen talks

djiuser_RIeSM3mAo5mf Posted at 8-14 06:35
Labroide I refer about Airplane mode ON which Stephen talks

Labroide I refer about Airplane mode ON which Stephen talks
That still makes no difference.
Airplane mode stops the phone from transmitting but doesn't stop it from receiving GPS data.

And you don't need to use Airplane Mode anyway.
It really doesn't make any difference to your flying.

archer180 Posted at 8-14 02:41
Good idea DJI Stephen.

Hi there archer180. You are very much welcome and thank you for the reply. If you have any other concerns or inquiries with DJI. Please feel free to post it here at DJI Forum. We are all here to help and support you. Thank you.