I don't think in this business giving your products for under cost is the way to go. Maybe offering the first month free and then charging your regular price is ok. We have seen offering discounts and posting them on forums, Twitter and Facebook are the best way to go.
Discounts, offers and promotions are the best ways to attract clients but its required to reach those offers to the client end and it can be done by forum posting, email marketing and through social media.