H1 to H4 to H1B change of status work start date?
You have to wait for H1B change of status approval to start work.
You converted from H1 to H4 status within US and now filing H1B change of status again. You should start work for H1B employer only after your status is changed to H-1B.
Your current status H4 will stay with you until the H1B application is finally approved by USCIS.
Small consulting companies might lure you to start working immediately on filing H1B, but, beware that you will be violating your H4 status rules and this can put you in USCIS bad books.
H4 to H1B change of status work start date?
In simple H4 to H1B case as well, where you filed H1B with change of status in lottery. You can start working on Oct 1 or the start date of your H1B as approved by USCIS.
The change of status happens automatically on the H1B approval date and you should START working i.e. your payroll should be run to keep you in H1B status.
If you do not start working on H1B after its approval, you are violating your H1B terms.
Even in case of H1B premium processing, you should wait for approval before starting work.
Can I work in H4 Status while my H1-B transfer is in progress?
As answered above, you CANNOT work on H4 status unless your H1B is approved and status is officially changed to H1B.
You will get a new i94 on your H1B transfer approval which will correctly show your H1B status.
H4 EAD to H1B transfer, Start work on Receipt date?
You can apply for H1B transfer while on H4 EAD.
Since you are on H4EAD work permit, you can keep working on H4EAD status until your H1B transfer is finally approved and your status is changed to H1B.
Until you get the new H1B transfer i797 approval with new i94, your status will still be H4 and work authorization with H4EAD.
H4 to H1B cap exempt
You had an approved and stamped H1-B visa from outside USA which was never utilized. You quit the H1B sponsor employer and came to US on H4 visa as a dependent.
Now, a consulting company here in US filed a cap exempt H1-B transfer I-129 through Premium processing.
The consulting company has informed you that you can start working immediately after filing the case to USCIS i.e. even before getting the approval of H1 status.
DO NOT START WORKING based on H1B receipt if you are currently on H4 status.
It is not legal as your status does NOT change until USCIS approves it.
In this case, do NOT listen to consulting company as they just want to make money.
Since, you do not have a valid SSN and H1B work permit, you will be violating your H4 status rules.
DHS takes visa status violations seriously and can deny your other visa application in future.