Nigel Short lost when his phone gave out a 'battery low' warning at Liverpool 2008: see
http://www.liverpoolchessinternational. ... ts_rd2.htmAt a much lower level, after obeying an instruction to turn his phone off, one of Nottinghamshire's Under 11s lost when the phone issued an alarm set for some long-forgotten purpose.
If Nigel Davies' phone simply beeped, I'm not sure how that's different from the beep of a digital watch. One of those sounded loudly near my game on Sunday. (I'd quite like a rule that allows one to smash such a watch if it beeps. Once it's happened, you know that you're going to hear it again in 60 minutes time.)
The wording of the current law (Article 12.2b: 'If a player's mobile phone rings in the playing venue during play, that player shall lose the game') does seem to give the arbiter some discretion over the interpretation of 'rings'. However, in the laws that take effect on 1 July this year, this loophole has been closed; Article 12.3b says: 'If any such device produces a sound, the player shall lose the game'. So Nigel was probably lucky: FIDE didn't really say what they intended to say in 2005.
The 'not my phone' defence seems very shaky to me. If it's in the player's possession, it's his or her responsibility, regardless of ownership.