I don't think it would be discretional; A ceo that is fully reporting and decides to unofficially attend a conference call arranged by shareholders wouldn't be held under scrutiny. He communicates with many shareholders via twitter, linkdin and proly other sm platforms. This would be no different.

But if the ceo decided to hold his own conference call then I would think he would have to make it official to allow all common shareholders etc to attend at their discretion.

but I think we're taking this way out of context. it was just a call to get people on the same page about their understanding regarding the 8k. it's out there for everyone to read.