http://www.matityahu.org/RavLeffQA/viewquestions.asp?viewcat=17
its an audio 1 min answer to this question by Rabbi Leff with sources.
basically:
it is assur for women as well as men,
but the Chochomim instituted a Takana that women are allowed to talk to each other when in a public bathroom that men might enter, so that men will be aware of their presence.
seems he says we dont poskin that way in public bathrooms today
but i THINK i heard in the past that women ARE allowed to talk in bathrooms in homes
probably its not a simple answer like most things in Halachah