Valid H4 and H1 I797 B approval


I am in India and I have H4 Visa (valid from Oct 2012 till sept 2015) stamped on my passport. I applied for H1B in 2013 and it got approved. I received I797B (stamping required) but have not done stamping. Presently I need to travel to USA and have following questions

  1. I received H1B does it mean H4 is no more valid to travel to USA?

  2. If i travel to USA on H4 without H1B stamping done on my passport, does it will make my H1 B void?

  3. Suppose I travelled to USA using H4 then can I get my H1B transferred to another company/client (different location)? If yes, then will it require me to travel to India for stamping before I start my worl with new company?