Something

        SELECT
                SUM(c.billsec/60) AS ttime,
                COUNT(c.uniqueid) AS tcalls, 
                CONCAT(e.FIRST_NAME, ' ', e.SECOND_NAME) AS emp,
                IF( c.userfield = '', c.src, c.userfield) AS ext
        FROM
                cdr c
        LEFT JOIN
                extentions x ON (
                          c.src=x.channel OR c.userfield=x.extention
                )
        LEFT JOIN
                employee e ON (
                          e.extention=c.src OR e.extention=c.userfield
                )
        WHERE
                c.lastapp = ?
        AND  
                c.disposition = ?
        AND
                c.accountcode LIKE ?
        AND
                (
                          (
                                    c.src BETWEEN ? AND ?
                          )
                          OR
                          (
                                    c.userfield BETWEEN ? AND ?
                          )
                )
        AND
                (
                          c.calldate BETWEEN ? AND ?
                )
        GROUP BY
                IF (
                          c.userfield = '', c.src, c.userfield
                )

-----------------------------------------------------------------------

Changed to:

        SELECT
                SUM(c.billsec/60) AS ttime,  
                COUNT(c.uniqueid) AS tcalls, 
                CONCAT(e.FIRST_NAME, ' ', e.SECOND_NAME) AS emp,
                IF( c.userfield = '', c.src, c.userfield) AS ext
        FROM
                cdr c
        LEFT JOIN
                extentions x ON (
                        IF (
                                c.userfield = '', c.src=x.channel, c.userfield=x.extention
                        )
                )
        LEFT JOIN
                employee e ON (
                        IF (
                                c.userfield = '', e.extention=c.src, e.extention=c.userfield
                        )
                )
        WHERE
                c.lastapp = ?
        AND  
                c.disposition = ?
        AND
                c.accountcode LIKE ?
        AND
                (
                        (
                                c.src BETWEEN ? AND ?
                        )
                       OR
                        (
                                c.userfield BETWEEN ? AND ?
                        )
                )
        AND
                (
                        c.calldate BETWEEN ? AND ?
                )
        GROUP BY
                IF (
                        c.userfield = '', c.src, c.userfield
                )