Hello All,
Brief History: I am working for a Food Processing company (A) in R&D. Company A was my sponsor for GC. I have been on EAD since Oct 2007 (filed 485 during July-Aug 2007 time period)

. My I-140 was approved Jan 2007. My GC application was started in Apr 2006 - Perm process. Also, i still have my H1B(Extension) valid until Apr 2010. Company A uses a consulting firm for roughly about 25 - 35% of R&D projects.
Reason to change: I believe this opportunity will have a significant change/growth to my career.
Questions: 
Can i change my job to the consulting firm using EAD? What are the consequences i should expect from USCIS? Does the Consulting company have to get involved with any Immigration fillings?
If i decide to work for the consulting firm, i will still be doing the same job for Company A but as a consultant + I will have additional projects with other Food Processing companies. I think labor application job description won't change (Company A to Consulting Firm) and this is where i struggle to understand the rules. Need your thoughts and Advice.
Appreciate your help and Thanks for your time.