How does Ice make drinks Ice cold?

Ice, in it's solid form, is at a maximum temperature of zero degrees Celsius. You might expect that a small volume of Ice might cool say a 25 degree drink to somewhere halfway between 0 and 25. This is not observed, because Ice, in addition to absorbing heat as it gets warmer, absorbs heat energy when it changes phase from solid to liquid. This is known as the specific latent heat of fusion, which is defined as: The amount of energy required to change the state of a substance from solid to liquid at a constant temperature, which for water is 334000 Joules per Kilogram. During this entire process the Ice remains at 0 degrees, and the surrounding water is kept just above this temperature until all the Ice has melted, provided there was a sufficient amount of Ice to cool the entire drink to just above zero before it had all melted.
Separately, Ice is very effective at cooling drinks quickly because convection currents are set up in the container, and quickly the entire drink becomes the same temperature.