H1b transfer before stamping or after stamping

Hi all,

I have got h1b approved from company A and planning to go for stamping next week. My current company B wants to send me to u.s. Ford a short term visit as I hold valid B1. They have also told me that if I have h1 then can send me for a long term. So now I am in dilemna that should I inform my current company that I am going for h1 stamping or not. If I get stamped can company B send me or they need to file again petition and do I have t go through again visa stamping ? I have got h1b approved notice from company A.