The federal Government recommends that all Australians travelling to Vanuatu register their travel details with DFAT before they depart. You can register online at http://www.vanuatu.highcommission.gov.au/. There are hospitals on different islands. If you require treatment, it is expected you will pay in cash even if you have medical insurance.
For serious health issues you can be evacuated to Australia or New Zealand. There is a service in Vanuatu staffed by Australian and New Zealand medical staff. More details are found at www.promedical.com.vu.
Emergency numbers may change, so please do your own checks on this. However, at the time of writing, the emergency numbers are: