From the Keith Baker FAQ thread on WotC boards:Nihm said:Hey All, I was playing a Changeling for awhile and I love it. But recently I looked at the rules and noticed the ablity was like using disguise self. Does this mean that my voice does not change to fit the new forms? If so how can I get around it, besides keeping my mouth shut.
Q Originally posted by Yago Aginor How functional are the changes to sex(gender) introduced by a changeling's changing ability?
A Absolute. A changeling's gender is its default that it will revert to if it, for example, dies. But a "male" changeling could actually assume a female form, become pregnant, and carry a child to term (it loses the ability to shift gender while pregnant). This will be covered in more detail in Races of Eberron.
Would Var's voice change enough for him to safely pass for a girl?
He'd get a -2 to his Disguise check, but that's what the +10 bonus is there to offset. Yes, change in voice is part of the transformation.

(Dungeons & Dragons)
Rulebook featuring "high magic" options, including a host of new spells.