There are a lot of people discussing the impact of using AP on H-1B status, and the issues about EAD. I inquired my immigration lawyer (He is also a professor in the law school of my previous university). Here is his answer:
1.After using AP, you’re no longer on H-1B status. Instead you’re on I-485 pending. All the topics after this are about your I-140, I-485, etc. No H-1B status existing anymore, of course no transfer/extension for it.
2.You must use your EAD to work after using AP, even if you continue working for the same company.
3.The advantage of using EAD is that, you can change your job. But if you don’t want to waste your time, please DO NOT do this until your I-140 gets approved, and 6 months have passed since you get the receipt from INS for your I-485 application. Otherwise, you will have to prepare all your new I-140 and I-485 application materials from the very beginning. Also for those people who concurrently file I-140/485, don’t take the risk of changing the job even 6 months from the day you get the receipt from INS.
Good luck to every one !