Tightslot,
Your understanding is correct. Strange as it may seem, the engineering fraternity responsible for mobile 'phone standards are generally against any mobile 'phone use because it's so annoying - and they spend a lot of time flying! I was told by a CAA guy that ICAO had come out against it because of fears of 'aircraft rage'.
The difficulty is that because aircraft age and wiring harnesses chafe and the shielding of cables decreases, an aircraft that was OK when new may not be two or three years later. Typically, a 737 has about 70 radio antennas of various sorts, scattered around it. Now you can hear on R/T the 'ticking' caused by a mobile 'phone, but you could have the radio altimeter go unhappy, or the ILS receiver or the VOR, and you would know (maybe) that there was a problem - but not what. If you were doing a CATIII autoland, you certainly wouldn't want any chance of the altimeter going t*ts up!
So having reported as a fault that something didn't work, engineering would get involved and the result would be 'no fault found'.