Please help! H1B extension at the 5th year with I-140 approved i

Laid off in Jan 2009 in Company A with approved I-140 (EB2 PERM), then, Company B transfered and extended my H1B which is valid until March 2012, my H1B 6-year term ends September 2012.

Questions:

1. I heard that I could extend my H1B another 3 years as long as the visa number is not current when I file the applicatioin no matter if Company A revoke my I-140 or not, is this correct? some people said I cannn't if the company revoked my I-140. But I-140 can not be revoked unless it is fraud, so in practice, none fo companies would like to revoke an approved I-140, is my undersatnding correct?

2. If I can extend my H1B, what are the earlist and latest dates to do it?

3. I am corrently in Company B, if I go to Company C this April, Can my H1B be transfered and at the same time extended to March 2015? or I have to extend it to September 2012, and then do anthoer 3-years extentsion in the future?

Thank you very much in advance!