I agree, the solution with the Wi-Fi and mobile data is not convenient for the user. However, with time and some training, it is doable.
You can either use the official RICOH THETA mobile app (which is free) to take the image and transfer it to the phone, or you can write your own app. The image on the phone is exposed as a URL endpoint. Unfortunately, you can’t pull the image directly from the camera to your server. The mobile phone will need to pull the image to local storage, then push it back to your server once it re-establishes mobile data. This is likely not as convenient you want, but it’s a limitation of mobile and wifi traffic on Android phones for security reasons.
More information about this problem is below