@Nath

The issue is the guarantee that Optus have with the government regarding the infrastructure they have installed; it involves their provision of access to 000.

That must not be interrupted and mitigations must be in place to route around any disruption, extending to cross connecting to other infrastructure providers without delay. Only if all carriers are involved (eg. natural disaster taking out an areas cell towers) does the liability reduce. They're still required to re-establish connectivity as soon as possible though.

In failing to meet that guarantee, they're liable for severe penalties.

And no, as infrastructure providers involved with 000/112, they can't up stakes and leave just because they feel like it.

(Ex-PMG/Telecom/Telstra bloke)