Whether the milk is cold or hot or mixed with something else is not the issue, you will get the same amount of calcium based on the volume of milk.  If the amount of milk you get is the same, then the calcium will be the same.  However, milk is not always the best source of calcium.

You can also get calcium from sardines, fortfied breakfeast cereal, soya beans, tofu, soya drinks, dried figs, rice pudding and baked beans.

I hope this answers your question.