Quote Originally Posted by Divinus Arma
(2)There were no phalanx of Hastati, Principes, and Traiarii. The Triarii were the only ones who fought in phalanx, and they did so with the Hasta.

An additional point on the Hasta: Prior to the Spanish campaign in the punic wars against Carthage, The hastati primarily used the Hasta (From where they derive their name). It was after the spanish Campaign that Hastati and Principes took the Gladius as their primary weapon in addition to the Pila.
I believe the gladius simply made an earlier sword design obsolete. I seriously doubt the hastati/principes used any spear-type object other than javelins. As for the Phalanx? hmmmmm...there's been some discussion, here, that points to the romans seriously dropping "true" phalanx functions (debatable)