Entering into US on H4 with H1B approved petition and then filing change of status

[seattle12]

Hello

I have a valid H4 VISA till March 2013. I was living in USA on H4 visa till 2011 December and then came back to India. I have 6+ years of valid work experience and managed to get a sponsorship from a USA based consultant company to file H1B this year and i am waiting for the H1B petition to be approved. Since i was outside USA when H1B was filed i will not get i94.

I will be travelling to USA next week on H4 VISA.

I would like to know my option to start working as soon as the H1B is approved.

1) Is it possible for me to apply for change of status from H4 to H1 without going for stamping?

2) Is it allowed to file change of status in this case?

3) Is it mandatory to go outside USA and get stamping done in my case?

Thanks