i was looking on a vx site and some one on there had the same problem, and some one said make a call on a mobile and press the button the fob should interfere with the sound on the call or make the screen flicker. as he found out it was the fob not working doing it this way, and took the fob apart and found a dry joint on the micro chip, his is working now. might work doing this i dont know.
The fob isn't on same frequency, and I very much doubt that a licence free band would be on a harmonic of the cellular bands.
Thus this sounds like that "a bloke down the pub said" 'dangle berries'.
Sounds similar to the one where if your locked yourself out but got a spare key at Home, phone home using your Mobile, get the other person at Home to operate the Fob near the Mic, hold your Phone against the door lock of the car and , hey presto, the car is now unlocked.
Doesn't work on Land Line phones as no Radio signals involved of course.

The power of Radio Waves

not that I would know anything about that sort of thing.