In corporate world, there is often misunderstanding that people need to improve on communication skills.
Communication is the externalization of how we observe, sense, understand, organize, think and believe by leveraging language. 

It's too general and often confusing to say communication skills.
If people don't speak up, maybe it's due to lack of trust.
If they talk lengthy, maybe they are incapable of extracting key information.
If they use too much jargons, maybe they don't understand things deeply.
There could be all kinds of underlining problem that makes us feel that it's communication issue. 
e.g. lack of knowledge or context, culture/religion difference, people just don't care, conflict of interest, ego, emotional, don't know the audience, unaware of assumptions, no deep understanding, lack of structure, etc.

To improve communication, it requires careful observation about the gap and ask a few why to figure out the underlining problem. Until then, expecting significant improvement on communication is going to be disappointing.