SMS open rate is 98% compared to only 20% of emails. DSIM says that SMS marketing gives 7 times higher effect than email listing. Our 18 years background in mass SMS texting says that this is one of the best ways to increase sales. To reach out to the audience, you should obtain a list of their phone numbers. But watch out! Some methods can even lead to a judicial proceeding. In this article, we will tell you how to collect client phone numbers for text marketing in a legal way and what GDPR says about it.