The WNB prefix means that it is an custom application specific hybrid (as in "thick film on ceramic") module, that pretty much means that there never was any kind of documentation for the part. Obviously the function of the thing is that it implements what is called "phone hybrid" (completely different meaning of "hybrid") in solid state without magnetics.
Looking at schematics of what is inside the handset it seems to me that it does not even make much sense to think about a pinout of the thing, because most of the pins are used to connect external components that could not be efficiently integrated into the module (essentially a handful of capacitors and overvoltage protection network).
Given the peer comment with the schematic, it does feel like there's more you can gather. It appears, for example, that there's a "push to amplify" button on the handset that's not pictured in the post...it doesn't show the other side of the handset where that button probably is.
Shown as "-( 21 S 22 )-" on the schematic, bottom left. The wedge shaped metal tab you can see on the backside of the open handset is probably the spring+contact for that switch? So the IC also appears to have an amplifier.
The "-( 21 S 22 )-" thing is a speaker in the handset. The button is above that, labeled "VAR.".
Probably the main reason why essentially the entire electronics is in the handset and why it is somewhat complex is that it does not use carbon microphone, but the microphone is actually the exactly same part as the speaker, used as an dynamic microphone (with the required amplification being done by the hybrid module).
Looking at schematics of what is inside the handset it seems to me that it does not even make much sense to think about a pinout of the thing, because most of the pins are used to connect external components that could not be efficiently integrated into the module (essentially a handful of capacitors and overvoltage protection network).