I-485 Pending H1 transfer

2004 July PD, 140 approved, 485 pending after 180 days, current H1B valid through the 2010. Worked for company A over 5 years, got an offer from company B with the better pay and higher title. If company B file the H1 transfer for me and get approved, can I turn done the company B'job and still work for company A? The reason being is company A matched the company B's offer. Please advise. Thank you very much!