I was just surfing around for general flights and this one came up:
It says the plane is owned by AirTran, but it does not have the conventional flight numbers for a commerical flight or charter. I am assuming with the unique cities in its history that is is still in post-delivery (testing, painting, etc.) phase and has not yet begun regular service.
The only other guess is that this is owned by the airline, but is kept for corporate travel, etc.