Second thing, as a free member I can't respond to IM's. I think you should add a note to anyone IMing a free member that I'm a free member and can't respond. Otherwise I look rude.
1. You could reply during Happy Hour when free members have all the features of a premium subscription.
2. All someone has to do is look at your profile to see that you are a free member. As a rule, if I have never responded to anyone before, I always look at someone's profile to see not only their membership level but also what boards they have posted on. Sort of like "Know who you are replying to".