So this isn't what the requester was asking for but it is the answer to "SQL selecting rows by most recent date".
Modified from http://wiki.lessthandot.com/index.php/Returning_The_Maximum_Value_For_A_Row
SELECT t.chargeId, t.chargeType, t.serviceMonth FROM(
SELECT chargeId,MAX(serviceMonth) AS serviceMonth
FROM invoice
GROUP BY chargeId) x
JOIN invoice t ON x.chargeId =t.chargeId
AND x.serviceMonth = t.serviceMonth