Ok, time to throw my hat in the ring:
First, according to my PHB (first printing) Charging does *not* provoke an AoO.
Second, Charging is a "Special" Standard Action as described in the very first line of the "Charge" section. Yes, you attack, but in the description it does not say "you perform a melee attack" action; you do not perform "an attack action". So, in my mind this would mean that the entire act of charging is a standard action, even though you attack. Thus it is "special".
Third, Spring Attack says in it's description "...when using the attack action...". OK, check out what a Charge is, it's not an attack action, it is a standard action.
So, there ya go. No spring attack with a charge.