Question: For all phone numbers, what percentage of the total is cell phone?
SQL: SELECT CAST(SUM(CASE WHEN T2.Name = 'Cell' THEN 1 ELSE 0 END) AS REAL) * 100 / COUNT(T2.Name) FROM PersonPhone AS T1 INNER JOIN PhoneNumberType AS T2 ON T1.PhoneNumberTypeID = T2.PhoneNumberTypeID