Everyone plays on the same client now, regardless of what expansion you have, adding expansions just "unlocks" that expansions content.
All you should have to do is add the authentication code that came with the game to upgrade your account level to MoP and you should be good to go.
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Threats of violence. We take these seriously and will alert the proper authorities.
Posts containing personal information about other players. This includes physical addresses, e-mail addresses, phone numbers, and inappropriate photos and/or videos.
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