I can change the field that is displayed as a title in the activity history? Currently is the subject:
As manjit mentioned, you cannot change the existing value. However you can try below workaround.
- Use workflow rule to update subject value from 'No subject' to any value defined in workflow field update.
- Select any default value from lov's on Subject field.
- Else you can manually update.
Was able to achieve using WF.