The top 5 most critical communication skills for a Project Manager are:
1. Effective writing - using clear, unambiguous, non-threatening, commonly understood English (the technical language of business worldwide)
2. Listening - not just hearing but truly listening to what the speaker means
3. Compassion/Empathy - being able to manage a project team while at the same time being empathetic to life's incredible unplanned "emergencies" that crop up when dealing with people
4. Passion and enthusiasm that inspires the team to row the boat all in the same direction.
5. Avoid always being status quo, during any enterprise project you must stand your ground and take decisions that you believe is in the best interest of your project. (Avoid Group Think sometimes its hard and usually creates costly overruns)
Really a combination of all the above mentionned is required but demonstrating your passion in effort and quality will garantee a great team approach and may create a high performance team.
A Forrester study states, 60-95% of defects in delivered interfaces can be traced directly back to poor requirements, and 40% or more of a software developer's time is spent doing rework. Use a prototype approach or methodologies like SCRUM that forces both parties to speak to each other at a regular shorter time interval.