Too bad CA isn't in the nurse licensure compact or your CA license would be good in MS too. Check with the Mississippi Board of Nursing http://www.msbn.state.ms.us/
This comes from a section of our textbook: " When [foreign] nurses move to the United States, they must show evidence of completing their original educational program and restrictions of their license. In addition, nurses need to demonstrate competency in English and the ability to take and pass the NCLEX-RN examination. Foreign nurses take a special examination administered by the Commission on Graduates of Foreign Nursing Schools. The examination in given in English and tests the knowledge required to practice in this country. On successful completion, the foreign nurse graduate may apply for a license to practice in this country."
So if you've taken NCLEX you might not need all the other junk I wrote about but I hope that helps. Mainly contact the MS BON and they'll answer your specific questions.