The sole published source for the language is Donohue and San Roque (2004) (see references), although the authors of this have also Identified I’saka material in Donald Laycock's unpublished fieldnotes.
Isaka is spoken in Krisa and Pasi villages of Bewani/Wutung Onei Rural LLG in Sandaun Province, Papua New Guinea.
There are the following consonants in I’saka: The sounds [p], [ɸ], and occasionally [f] are heard in non-contrastive free variation, making them reflexes of a single phoneme (transcribed p).
Donohue and San Roque (2004) suggest that there was an earlier phonemic or allophonic contrast which is in the process of merging, perhaps under the influence of neighboring languages and Tok Pisin.
(These are spelled bou and mou; after other consonants, nasal vowels are spelled with a final -ng: that is, voiceless pa, pang, ta, tang, ka, kang, voiced stops ba, ma, da, na, other sa, sang, wa, wang, ya, yang.)
Nouns do not have case marking in core grammatical roles, although there are suffixes for Instrumental, Accompaniment/Location and Predicate possessor.