In order to get to Uldum you will need to do a few quests in the zone before the portal will be available to port to Uldum from Stormwind (SW) or Ogrimmar. Specifically this quest Impending Retribution is the one that has to be done. You will get the first in the chain after finishing a few simple collection / kill # of quests.
Detail For Alliance
Pick up Hero’s Call: Uldum! from the Hero’s Call boards parked around Stormwind when you turn 83. While it is believe that this quest has bug at the moment so you wont be able to use the portal from the Earthshrine to get to Tanaris, so get a portal to Dalaran and use the Caverns of Time portal OR try to get a mage to port you to Theramore and then fly to Tanaris. After a few steps you will be escorting a caravan in a quest called Easy Money which after a movie sequence will deliver you (in a cage so word to the wise, do not be shapeshifted or mounted when you accept this quest) to your new quest hub.
After that, the port to Uldum will show up in Stormwind (SW) or Ogrimmar.