You can pick up your allotment of magazines without paying for them. You say how many copies of each issue you want, and then you pick them up when they come in. (At least that's how it was 3 years ago, and it doesn't sound like it's changed.)
HOWEVER, it will quickly become apparent if you're one of those that gets mags but doesn't pay for them. Among JW's, appearances are EVERYTHING. So it is definitely in your best interests (if you wanna be thought of as a good little dub) to walk directly from the literature counter to a contribution box and drop something in.
And while it isn't tracked on a per-person basis, the congregation as a whole is expected to send in contributions to the Watchtower. If those contributions are below some threshold, they can expect a special needs part from one of the elders on 'takin' care o' business'.
So there's free, and then there's "free".
Dave