In zombies map "five" the teleporters do serve a purpose.
Two main purposes really.
first one is that zombies can go into the teleporter from one side of the map close to you, so you dont have to run around trying to find the last alive zombie, wating money going up and down elevators
Second one is, that in the war room you will see five switches with "defcom" beside them. After you turn on electricity, you can activate these switches. After you have done all 5, all teleporters lead to the presidents room, where you will find the Pack-a-punch machine to upgrade your weapons, making them more powerful.
Its really really important you get a weapons upgrade to survive the harder levels.
No, theres no ending.