@hprice20, Usually, there's no source field associated with which one has updated the blacklist SMS field (Any blacklist fields). You will have blacklist fields and corresponding lastmodification datetime. In general, you can audit the following anything is updated the SMS flag,
- Data Import workflow
- Any landing pages that are updating the flag.
- preference center if SMS included
- Custom data/campaign management workflow
- Handling SMS keywords
Thanks, Sathees