I've spent my entire career in I.T. as a programmer, an analyst and a project manager and have found the following communication competencies to be essential:
1) The ability to interview subject matter experts using active listening techniques
2) The ability to frame an issue or problem succinctly
3) The ability to define a process flow, particularly a swim lane diagram
4) The general ability to visually depict complex concepts
I'm sure others could add to this list, but these four competencies might be a good starting point.