Vowels

Iaai has ten vowel qualities, all of which may occur long and short. There is little difference in quality depending on length.^[4]

Iaai constitutes one of the few cases of front rounded vowels attested outside of their geographic stronghold in Eurasia,^[5] even if other cases have since been reported in the Oceanic family.^[6]

The vowel /ø øː/ is only known to occur in six words. In all of these but /ɲ̊øːk/ "dedicate", it appears between a labial (b, m) and velar (k, ŋ) consonant.

After the non-labiovelarized labial consonants and the vowel /y yː/, the vowel /ɔ ɔː/ is pronounced [œ œː].

The open vowels only contrast in a few environments. /æ æː/ only occurs after the plain labial consonants and the vowel /y yː/, the same environment that produces [œ œː]. /a aː/ does not occur after /ɥ ɥ̊ y yː/, but does occur elsewhere, so that there is a contrast between /æ æː/ and /a aː/ after /b p m m̥ f/.

The vowels /i e ø a o u/ are written with their IPA letters. /y/ is written û, /æ/ is written ë, /ɔ/ is written â, and /ɤ/ is written ö. Long vowels, which are twice as long as short vowels, are written double.

Consonants

Iaai has an unusual voicing distinction in its sonorants, as well as several coronal series. Unlike most languages of New Caledonia, voiced stops are not prenasalized.^[4]

Unlike many languages with denti-alveolar stops, Iaai /t̪, d̪/ are released abruptly, and /t̪/ has a very short voice onset time. However, the apical post-alveolar and laminal palatal stops /ʈ, ɖ, c, ɟ/ have substantially fricated releases [ʈᶳ, ɖᶼ, cᶜ̧, ɟᶨ], and may be better described as sounds between proper stops and affricates.

The labial approximants are placed in their respective columns following their phonological behaviour (their effects on following vowels), but there is evidence that all members of these series are either labial-palatal or labial-velar. /ɥ̊, ɥ/ are sometimes pronounced as weak fricatives [ɸʲ, βʲ].

In many cases, words with voiced and voiceless approximants are morphologically related, such as /liʈ/ "night" and /l̥iʈ/ "black". /h/- and vowel-initial words have a similar relationship. The voiceless sonorant often marks object incorporation. However, many roots with voiceless sonorants have no voiced cognate.

The labialized labials are more precisely labio-velarized labials. There is evidence that non-labialized labial consonants such as /m/ are palatalized /pʲ/, /mʲ/, etc., but this is obscured before front vowels. If this turns out to be the situation, it would parallel Micronesian languages which have no plain labials.