I am on H-4 (spouse) visa and my visa expires on September 30th,2015. We have applied for premium processing of visa extension and expect to get it done within 15 business days. But I am hoping to enter U.S. from my country by September 19th and I am afraid I may not have the time to get the stamping done by 19th. Can I still enter U.S. without stamping the visa since my visa does not expire until the 30th? Or will I be turned away at the port of entry because I did not get it stamped after a visa extension has been granted?
If you have a current valid visa you can enter using it. However, when your time on it has run out, you have two options to switch to the new visa:
The first: simply leave for 24 hours and then re-enter using the new one. (Plan a quick trip to Canada, Mexico, or the Bahamas, depending on where you are). You can then re-enter using your new valid visa.
Second, you can apply for an extension of your current visa, or permission to switch visa types. You can find more information about those options HERE and HERE. It is unclear to me if you can change (transfer) your status to an already existing visa.