DEREKL,
You are absolutely right - it is not so much the interference with the onboard systems, but with the cellular multi-station ground network, which have have nothing to do with the operation of the flight!
But if the regs say 'no phones on during flight' (and taxiing is already part of the 'flight') then those damned things should be off - even if it is only in the interest of the fellow passengers!
A PA asking the passenger in seat XX to switch off his cellphone usually works wonders!
Cheers,
Ikarus
P.S. Fortunately, our onboard electronic systems are much more resistant to interference than the legislators may think. But so what...safety is no accident!