I did my Masters in Biomedical Engg from US university in 2007. Currently I am working as a research enggg for a non-profit research Institute in California. I have H1 which is valid till 2010. However, I am planning to go back to university and get my PhD. I have partial scholarship from the university, but I can get it only if my status is changed to F1. The new quarter starts in September '08. If I apply for change of status from H1 to F1 it might take more then 2-4 months. Instead can I go to US consulate mexico/canada with I-20 and supporting documents to get my F1 stamped. However, If for some reason they reject my F1 can I still enter US on my H1 which is valid till 2010 as I still have a job in US and planning to resign only if I get my F1. I would really appreciate if you could give any inputs.

You may have 2 different visas but you can use only one at a time.
Why make things complicated... just file I-539 while you're in US.

Hi... I really appreciate you responding to my question. The reason I cannot file I-539 for change of status in USA is because it might take 2-4 months, and my semester starts september'08.
What I am really concerned about is, If my F1 gets rejected at the US consulate, can I use my H1 to enter USA.