A few people have mentioned it already that one cannot assume they are kosher, and I am betting that probably they are not.
I know Lubavitch go out to have people put on tefillin. They approached me last Sunday, with baseball cap, at Six Flags. They may even give a pair away, although I am not promising.
And to avoid controversy about Lubavitch, to me they are wonderfully Jewish and do wonderful kiruv to those severely unaffiliated in the most remote of places.