Numbami (also known as Siboma or Sipoma) is an Austronesian language spoken by about 200 people with ties to a single village in Morobe Province, Papua New Guinea. It is spoken in Siboma village (7°30′47″S 147°18′04″E / 7.512985°S 147.301128°E / -7.512985; 147.301128 (Siboma)), Paiawa ward, Morobe Rural LLG.

Numbami is a phonologically conservative isolate within the Huon Gulf languages, and is the last Austronesian language on the south coast of the Huon Gulf. Its nearest relatives along the coast to the southeast are 270 km (170 mi) away, Maisin and Arifama-Miniafia in Oro Province (Northern Province in the former colony of Papua).

The word order typology of Numbami and the Huon Gulf languages is subject–verb–object (SVO), which is typical of Austronesian languages; while that of Arifama-Miniafia and most of the Papuan Tip languages is subject–object–verb (SOV), which is typical of Papuan languages. Maisin has been characterized as a mixed language, with both Austronesian and Papuan features that obscure its primary heritage, and there is evidence that settlements of Austronesian speakers along the 270 km of coast were gradually absorbed into inland communities speaking Binanderean languages (Bradshaw 2017).

Numbami distinguishes 5 vowels and 18 consonants. Voiceless /s/ is a fricative, but its voiced and prenasalized equivalents are affricated, varying between more alveolar [(n)dz] and more palatalized [(n)dʒ]. The liquid /l/ is usually rendered as a flap [ɾ]. The labial approximant is slightly fricative, tending toward [β], when followed by front vowels.

Prenasalized obstruents only occur in medial position, where the distinction between oral and prenasalized voiced obstruents is somewhat predictable. Medial voiced obstruents are statistically far more likely to be oral in words beginning with oral voiced obstruents, while they are far more likely to be prenasalized in words beginning with anything else. If denasalization of voiced obstruents is an ongoing change, one can track its progress through different lexical environments: it is 100% complete in word-initial position (as in bola 'pig' and buwa 'areca nut'), 80% complete in the middle of words beginning with voiced obstruents (as in bada 'market' and dabola 'head' vs. zanzami 'driftwood'), 35% complete in the middle of words beginning with approximants or vowels (as in ababa 'crosswise' vs. ambamba 'handdrum' and waŋga 'canoe'), not quite 20% complete in words beginning with voiceless obstruents (as in kaze 'left side' vs. kaimbombo 'butterfly' and pindipanda 'flea'), not quite 5% complete in words beginning with nasals (as in nomba 'thing' and -mande 'to die'), and not attested at all in words beginning with liquids (as in lenda 'nit' and lindami 'lime spatula'). (See Bradshaw 1978a.)

Although Numbami is phonologically conservative, it retains very little productive morphology, most of it related to person and number marking.

Free pronouns occur in the same positions as subject or object nouns. They distinguish three persons (with a clusivity distinction in the first person) and four numbers (Bradshaw 1982a).

Genitive pronouns also distinguish three persons (plus clusivity) and four numbers (Bradshaw 1982a).