Kudos for trying to innovate and add a new dimension to the game. Consider looking into the many unofficial servers for voice chat like [tl;dr]. You might even find some people in the community willing to RP over voice.
Like Snak3 said, an official voice chat would create a big headache for admins generating a wave of new reports for trolling, harassment, swearing, etc. with the added difficulty of having no record of the offense as evidence unless the players are recording it themselves (unlike things that are typed out and the admins can read just about everything you type).
People are entitled to their RP within the rules and everything, but not everyone will enjoy having to manually mute guys voice acting shoujo cuties, blasting music, bad mic feedback, trolling with soundboards, arguing with their parents, tending to their infants, etc. or the storm of OORP "//wtf mute ur mic" in response.
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