I think this is a very important debate and there is a definate case for this being the thin edge of the wedge where self reliance on the fells is concerned.
Most runners enjoy the personal freedom of being self-reliant in races. For many, carryiong a mobile changes the nature and 'feel' of the racing experience. It also changes the nature of the race for those considering entering for the first time, or whether to compete in bad weather - 'oh well Ive got my phone if anything goes wrong'
Making carrying a phone compulsory is taking away a little bit more of the competitors responsibility for their own safety and putting it in the hands of the organiser. I think we should resist this. There will no doubt be cases where mobile phones can be used to make things safer - this isnt in despute - but that doesnt make it right to enforce taking them.
This could easily and quickly become the norm. Im sure race organisers when making decisions about safety in their race imagine the court case and whether their decisions will stand up to scrutiny in the event of the worse happening. How would a court view the fact that the Edale race makes mobile phones compulsory but 'your' race didnt? Why not? Does that make you negligent?
The 'thick end of the wedge' that could follow might be:
Compulsory to carry phones that have been tested, approved and work
Compulsory to carry rest of kit that has been approved/tested
Logical progression to GPS for navigation and positioning
Races only being 'licensed' in areas with mobile coverage
Race organisers having to pass courses in safety before organising a race
Marshalls having to pass courses in safety before marshalling a race
Runners to carry GPS tracking chip to help organisers locate them
It is no bad thing that these sound ridiculous to read - imagine them applying to fell running!!? The scary thing is that some have already been proposed and some already happen in other similar sports. We should resist these changes to preserve the self-reliant nature of fell running.