You don’t call another cell phone, you call a controller which calls the cell phone. It’s quite possible this controller would provide feedback to the user in the form of ringing sounds before the cell phone is actually reached and it’s also likely that some of the cell phones on the plane were still registered on the system so the system would think it likely that the cell phone could be reached.
The ring you hear when you call another phone is not generated by that phone, but by the telephone central office. It is a placeholder to let you know the system is working on finding the handset somewhere within its system. If it cannot locate the handset, or the handset is not answered, then you are sent to voicemail.