I have H1b through paper conversion. What happens to my b1/b2 visa?

[H1bb]

Hi friends
I came to US on a B1 visa. I now converted the visa through my employer to H1b. Its only paper conversion and the visa is not stamped on my passport.
My B1/B2 is valid till the end of 2013 and it is stamped on my passport.

What happens if I leave USA. Can I re enter on B1/B2 since I have it stamped on my passport???

Please help me in this regard

[txh1b]

You can enter on B1/B2 only if your purpose is inline with B1/B2. If you want to work on H1b, you need a H1b visa stamped prior to entry.