There are a few loan programs that will approve you at 620 but the majority have a 640 rule. The credit requirements for FHA are not just about your FICO score. You also have to meet the debt to income ratio requirements, you have to have a steady job for at least 2 years, no bankruptcy for 2 years and no short sale or foreclosure for the past 3 years.
I would suggest you speak with a lender to ask all your questions. They can give you much more detailed answers and talk to you about loan programs that will fit your needs.
You can speak with someone at your own bank by asking to speak to a loan officer, or you can call the lender I do a lot of work with. Her name is Cherie Bowen at Academy Mortgage. Her number is 343-1068. If she doesn't answer, leave her a message and she'll call you back and get you started.