Vanuatu has two providers of GSM-class mobile services.
SIM cards (prepaid) are abundantly available in Vila.
eg Bon Marche supermarkets and numerous agents around the place. Couldn't get a rate card out of the girl (she genuinely didn't know and didnt have any..but that's Vila for you :-) ) but I had already checked the rates online.
Vanuatu locals have definitely embraced the mobile phone revolution.
Even out in the villages..casually swinging a machete whilst on the phone having a yarn.
Is it cheap? Yes! You will find it useful for anything from booking taxis/drivers/restaurants/ rentals and events.
I bought a 500 VT card (about AUD six bucks) and that lasted easily a week. Calls are billed per sec, no flag fall and no minimum charge per call...puts all Australian operators to shame for price.
Even calling back to Australia was cheap! But don't expect data services (at least on prepaid).
TIP: Before you leave home, ensure your GSM is unlocked. You can also just buy a cheap phone in Vila.