Can you explain what / how you did this? How did it have a connection for you to do something on the phone remotely, if the cell service was off?
The steps I took, as I recall, were as follows:
1. Track the phone's location on Find my iPhone.
2. Put the phone in Lost mode using Find my iPhone.
3. Disable the account at my carrier.The phone was in this state when United called me at the number listed on the phone's home screen, so doing this must not wipe out the Lost iPhone message on the home screen.
4. Enable the account at my carrier.
After the last step Find my iPhone was able to locate the phone at United's L&F in terminal B. I do not believe I was able to locate the phone prior to turning the cell service back on.