Interesting item, Papua New Guinea?

[David]

It certainly is a slit drum of some type. Most of the garamut that i have seen tend to be a bit larger than this one though, so this might be intended as a nicely carved trade version.
Wooden slit drums like this are common in cultures all around the world. They are especially prevalent throughout Austronesia, Africa and Meso America.
https://www.youtube.com/watch?v=JASFJ6o2r6w