Ah gotcha. That would be Source.
Source is not configurable via the UI, and Kevin is right that you would need to edit the code to make this work. Additionally however you also have to directly edit the database structure.
Source is in the ost_ticket table and is an enum.
Something like:
"source' ENUM('Web','Email','Phone','API','Other') NOT NULL DEFAULT 'Other'
To add more sources you add them to the ENUM, and then you might also need to add the code to the product to handle the additional sources types.
