It's maybe worth noting that while the space is indeed large, it's not actually used for anything much. The human impact of turning of electronic devices is negligable, given there is no cellphone reception anyway. In Karoo (where most of SKA will stand, in South Africa) they indeed turned off a few radio towers for cellphones and the site is radio-free (you can only use computers in isolated containers) but it only affected a few farmers. Asking people to turn phones off in one plane is probably far more of a hassle :-)