When I visited the DoJ web site, I couldn't find anything on this, suggesting it's in very early stages, though my Nortel friends tell me that the DoJ is in an intensive data-gathering mode.
Here's my take.
This is a highly competitive market that is being transformed from a PBX-centric environment to one that is "UC as an application"-centric. The same is generally true for the contact center space. Looking at historical market shares is not useful.
New entrants are coming in many forms: Microsoft, open source, cloud computing, Skype-like offers. Enterprises have many ways of evolving their telephony and contact center environments.
The DoJ has not, to my knowledge, questioned Cisco's market dominance of 70% in the router space,. Why would the DoJ care about a much smaller share for Avaya-with-Nortel in the voice space.
The DoJ process needs to be wound up very quickly; otherwise it is actually discouraging competition, weakening Avaya's prospects and giving Cisco an advantage.