change of status from B-2 to H1-B

If you enter with the B2 visa, can a u.s employer file H1-b visa for you whilst you are in the country, or do they have to WAIT until you LEAVE the country AND THEN file.

If so why?

So for example one enters in Jan and the B2 allows the person or the POE accepts this for 6 months till June
Will the u.s employer have to WAIT and apply for the H1-b visa for that person in June/July AND IF SO How long until the H1-b visa is granted?

Personally I cannot answer that question. But you can check Visajourney.com for info (however, its mostly focused on I-129 and I-130). Otherwise I suggest to check the USCIS website, yahoo!answers (it can be very useful and lots of people use it) and kravitzlaw.com (good legal website, they have a whole section dedicated to visas and how to file a visa while under another status).

Leaving the "why" apart, you cannot switch to H1B from B2 from within the US.

CIA wrote:If you enter with the B2 visa, can a u.s employer file H1-b visa for you whilst you are in the country, or do they have to WAIT until you LEAVE the country AND THEN file.

If so why?

So for example one enters in Jan and the B2 allows the person or the POE accepts this for 6 months till June
Will the u.s employer have to WAIT and apply for the H1-b visa for that person in June/July AND IF SO How long until the H1-b visa is granted?