H4 to h1 change when can i start working

[needassit]

I was on h1 from march 2007 until sep 2009 .From oct 2009 until now i am on H4. Now a employer is ready to do the h1 .My question is when can i start working?

1. can i start working once the h1 is filed as i was already on h1 ? or do i need to wait until i get the approval notice ( I797 ) .

I would appreciate if some one could answer me.. i am badly in need of the information.Thanks in advance.

[JoeF]

You need to wait for the approval notice.