Its a fine balance between flying alone and having the possibility of calling the emergency services should that be necessary.
I have mixed views on lone flying and there are several issues.
Firstly, if you fly alone, you don't get the camaraderie from your club mates, equally it can be enjoyable flying on your own.
Secondly, if you do fly alone and have an accident, be it a bee sting, bite from a prop, heart attack or a fly in your eye, you don't have anyone to help you.
As for clubs and lone flying, its a difficult one. At my old club we had about 15 members and flew 3 times a week, so lone flying wasn't a problem. In my current club we have 85 members and fly 7 days, so the ability to have set times is difficult as many people choose to fly at the drop of a hat and don't necessarily know people to be able to 'buddy' with.
In terms of mobile phones, I remain to be convinced about their impact. If you consider that at flying shows such as Weston Park or Cosford there are several thousand people present many who have phones/tablets etc, so the potential RF 'noise' is substantial, together with radios, wireless PA systems etc. I would suggest that should mobile phones be present at a flying site, that they be left in pit boxes away from radio systems and not taken on to the flight line, as you won't be able to answer it while flying.