I was born and raised in Birmingham, AL and I do have a very southern accent. I remember one time I was at work and I had to call a number to a company. Well, the number turned out to be wrong but the lady on the other end was from Pittsburgh, PA. For whatever reason she couldn't understand anything I said. Now I talk on the phone for a living and when I talk to someone at work, I don't sound like I do if I was on my personal phone. But for whatever reason she couldn't understand me.
Now my wife was born and raised in Georgia. Graduated from Tuskegee and everything and if you was to hear her talk, you wouldn't know where she was from. She had an assignment in Los Angeles, CA and it took her co-workers 2 weeks to find out she was from the South. They all said, "but you don't sound southern at all". And when we go to to eat and she orders some waiter/waitresses will ask her, "and where are you from"? This happens all the time without fail.