H1B to F1 (in process), back to H1B?????

I was on an H1B - applied for change of status to F1 which is still in process with INS. Now I have got another job and want to change back to H1B.

1) Can I go back to work with just a receipt notice for the H1B taking advantage of the portability clause

2) Can I cancel my F1 visa petition mid-way and apply for a new H1B?

3) Can I apply for the H1B even while my F1 is being processed... I will have to apply for the H1B at a different service center.

Thanks much for the help.