Bargaining breakdown plagues bargaining in environments with incomplete information. Does communication help or harm? On May 23, 2016, eBay Germany's Best Offer platform introduced unstructured communication allowing desktop users, but not the mobile users, to accompany offers with a message. Using this natural experiment, our difference-in-differences approach documents a 14% decrease in the the rate of breakdown among compliers. Though adoption is immediate, the effect is not. We show, using text analysis, that the dynamics are consistent with repeat players learning how to use communication in bargaining, and that the messaging strategies of experienced sellers are correlated with successful bargaining.