Generally, entrance to Mundo can only be gained by knowing someone who is already a member of Mundo-- preferably an elite because then they'll give you access faster. Mundo is made up of several different groups, and entrance is limited, so if one group is already filled up you must wait until someone leaves/is removed from the group in order to enter.
You can check availability by calling Mundo's 24/7 call center. Phone number can only be acquired if you know the Gatekeeper.
Awesome Elite: Sorry, line's still busy. Check tomorrow...but HEY, the Rock group has space!