When properly prepared for freezing it can be kept for at least a year - depending on the recipe used.
If it's a 'straight up American b'cream' it's best kept in a glass jar in the fzr. I have used plastic containers but then your time is shortened - say about 6 months.
Depending on how much icing there is, I use the smallest container I can find - buy them at the $ store - get like 4 for a $, putting each color in separate container. Baby food jars are also great for this