I'm sure others will have better data but here goes:
717-2BD: original AirTran deliveries - Fleet #s 701 - 741; Reg. #s N940AT - 988AT?
717-231: ex TWA / AA
- Fleet #s 779 - 798; Reg. #s N901AT - N939AT?
717-2S7: ex Pembroke (VuelaMex) - Fleet #s 760 - 770; Reg. #s N989AT - N998AT
Plus N717JL is a -2BD and AirTran's 50th 717 registered in honor of Joe Leonard; it's Fleet number is 741.
I'm pretty sure about fleet numbers but I usually don't keep up with registrations (unfortunately they have nothing to do with each other).
I work for Southwest, but the views expressed are my own and do not necessarily represent those of Southwest.