Liam,
If no one answered their phone on G days (or was not contactable when not contracturally required) manning would be at--not below--contractural levels. Answering phones on G days effectively costs potential co-workers their jobs becuase when it's used as a matter of routine operations it is used to cover inadequate manning and inadequate contracts. In fact, answering phones and over-checking rosters/working G days actually contributes to roster instability because there's little penalty for NOT constantly changing rosters and it can always be juggled to be made to work.
An added benefit would be that pay would be set to what it should be given demand and whatever contract we were working under. There would be a reduction in "gray" areas and more objective pay for work--benefit to all.
NO ONE is advocating not pitching in and helping in times of bona fide crisis. And I think everyone here as professionals recognizes when this happens and is more than willing to as a team help out. Bona-fide crises are however rare--this type of operation has morphed from contingency to routine. As such, G day workers are an enabler of bad behaviour in all respects.