Guys works !!! Spark .500 - RC .300 - DJI GO 4 v4.1.5. You have to get an Android phone with 4.1.3 V25 unlocked (or v27) app.
First: Connect the phone with RC and then with the Spark. Enter the menu and activate the "US" Aircraft mode restarts Wi-Fi in FCC mode.
Second: Kill Android apps, Kill RC Kill Aircraft. Connect RC with iPhone .. turn on AC. Now, once connected, ask to change Wi-Fi to change Country, press cancel, and enjoy FCC mode for IPhone forever.