user: Question: What is the Purpose of the Callsign with a Freq currently of 4RPH?
Columns: ['Callsign', 'Area served', 'Band', 'Freq currently', 'Purpose']
Types: ['text', 'text', 'text', 'text', 'text']
Sample row: ['4AT', 'Atherton', 'AM', '4AT (National)', 'Commercial']
SQL:

assistant: SELECT "Purpose" FROM "Table" WHERE "Freq currently" = '4RPH';