safety Graeme. when people are using their phones they are quite often not concentrating on what is going on around them and in a live transition that can be dangerous with athletes running with bikes. also they may not hear marshal/ref/race director instructions. easier to have a blanket ban on these items than have exceptions. Ok to use phone if you leave transition having finished, DNF etc but not in.
as a ref I can categorically say that mobile phones are NOT allowed in triathlons for events racing under BTF rules - as Outlaw is. not only that, they are also not allowed to be used in transition before starting or after finishing. same goes for music players like iPods etc.