As I mention before, I changed from F-1 to H-1 last year. I got my H-1 status in Feb 2004, but I went to my home country to get the H-1 visa stamp in August 2004. So I would like to know for counting my H-1 status, is it the date that USCIS (the Immigration) approved (which is Feb 1st), or the visa issued onto my passport (which is in August)?

Kkm:

I would think it would be the approval day.

When did your employer begin to withhold Social Security and Medicare taxes? That would serve as an indicator.

My employer started withholding my social security tax and medicare tax from Feb 1 2001.

Then H-1 started on 1 Feb 2004.