With nearly three-quarters of European mobile subscribers using short message service (SMS) each month — and barely one-quarter using any other mobile service — SMS remains the one mobile marketing option able to deliver a large number of users. However, user reaction to SMS marketing is highly polarized: While some campaigns perform exceptionally well, in most cases users are much more likely to ignore marketing messages than to read and consider them. To ensure success, interactive marketers should follow the golden rule of SMS marketing: If you can't target a campaign, you shouldn't send it.