This study is testing a mobile health application (*mHealth app*) with booklets to help adults with **Sickle Cell Disease (SCD)** manage their health better. SCD is a blood disorder that can cause pain and other health issues. The study will see if using the mHealth app plus booklets reduces hospital visits or emergency room trips compared to only using booklets or standard care, which is general advice without the app. The study will last for **12 months** and involves three research centers. **Key Points:** - **Duration:** Participants will be involved for about 12 months. - **Visits:** The study aims to reduce emergency room and hospital visits. - **Eligibility:** Adults with SCD who have been receiving care for the past year and can understand English are eligible. This research will help understand if the app and booklets can effectively reduce health issues and costs for adults with SCD. Participants will be monitored to see if this new method is better than the usual care.