I've seen this question posted along with can you buy them on their own. After last night's visit to Games and Stuff I think I can answer some of that.
No, you don't need the cards to play. The rulebook, yes you absolutely need that, but not the cards. They are super helpful but not necessary. The rulebook has everything stat wise you need to play. The book has a full chapter on the US and Soviet forces and it has all of the stats for the current release and the force diagram charts and points values that you need to build a force. So the Team Yankee book is everything you really need to play using your own models.
The cards themselves are really helpful as they have all of the stats and special rules in one place so you don't have to stop game play to hunt down what the Hunter-Killer rule is as an example. That rule would be on the backside of your Cobra's card which is very handy!
Now there's nothing to say that you can't grab some index cards and write everything down or that you can't grab the cards from the net and print them yourself. In fact, Battlefront has these cards on their own site now for you to check out.
For example, you can grab the M113 cards from here:
link
And the M1s
Cobras here:
link
Granted, they are only the front side. A quick Google search can get you the reverse side.
Will they ever sell the cards on their own? The Battlefront guys didn't say. Who knows? But I bet someone will be selling them on Ebay sooner or later. You get them in every boxed miniatures set so I can see someone cracking open a few sets and selling the parts.
