Lets Talk Milk...

The best way to go about freezing breast milk is to designate a time of day when you will be able to pump for an extended amount of time uninterrupted. You can pump, store the milk, and be ready for when a time arrives when you don’t have time to pump and need to grab the breast milk and feed your baby ASAP. Some mothers may not have a time slot where they know they can pump uninterrupted so the chaos method works too. Just pump whenever you can squeeze in the time. Every little bit helps. Pump the milk into a bottle and then pour it into a special plastic baggie (see below). One easy way to get all of the breast milk in the bag without spilling it everywhere is to set up the bag in a coffee cup so that it forms to the cup and stays in place. This way it won’t spill everywhere.
The best way to store frozen breast milk is special small bags specifically designed for breast milk. You can buy the bags just about anywhere: the grocery store, online, etc. They are usually available in packs of 25 or so. The bags are durable and completely sterile. They are also free of chemicals unlike regular plastic baggies, so your milk will be kept clean and safe for your baby. Most of the bags come with a double zip lock top. Some have a twist tie top but those could easily pop open and the precious breast milk will spill everywhere, so generally speaking the zip lock bags are a better choice.
When the milk freezes in the bag you can press it flat which makes it great for storage because you can stack the bags side by side. Most bags allow you to write directly on the bag with a marker. This way you can put the date that the milk was pumped on the bag. Frozen breast milk is generally good for up to six months whereas breast milk that you leave in the refrigerator should be used within 24 to 48 hours.
When it comes time to use the frozen breast milk simply place the bag in a cup or bowl of hot water. It will warm the milk. Then pour it in the bottle and feed the baby. Remember when you are heating up your breast milk to never microwave it! Microwaving breast milk or any other food or liquid for an infant can leave hot pockets that the baby could severely burn its mouth on.

source: http://www.breastisbest.com/infofreezingbreastmilk.html