select
    count(*) as Callcount,
    case
       when datepart(mi, PBXqtime) < 30
          then dateadd(hh, datediff(hh, 0, PBXqtime) + 0, 0)
          else dateadd(mi, 30, dateadd(hh, datediff(hh, 0, PBXqtime) + 0, 0))
    end as time
from
    callcomplete
where
    CustId = '3100472'
    and PBXQTime between '11/1/11 0:0:00' and '11/30/11 23:59:00'
group by
    case
       when datepart(mi, PBXqtime) < 30
        then dateadd(hh, datediff(hh, 0, PBXqtime) + 0, 0)
        else dateadd(mi, 30, dateadd(hh, datediff(hh, 0, PBXqtime) + 0, 0))
    end

SELECT
    DATEPART(DAY, pbxqtime) AS [day], DATEPART(HOUR, pbxqtime) AS [hour],
    (DATEPART(MINUTE, pbxqtime) / 10) AS [interval], COUNT(*) AS Callcount
FROM
    callcomplete
WHERE
    custid = '3100472'
    AND pbxqtime BETWEEN '11/1/11 0:0:00' AND '11/30/11 23:59:00'
GROUP BY
    DATEPART(DAY, pbxqtime), DATEPART(HOUR, pbxqtime),
    (DATEPART(MINUTE, pbxqtime) / 10)

select
    count(*) as Callcount,
    DATEADD(minute,(DATEDIFF(minute,'20100101',PBXQTime) / 10)*10,'20100101')
from
    callcomplete
where
    CustId = '3100472'
    and PBXQTime >= '20111101'
    and PBXQTime < '20111201'
group by
    DATEADD(minute,(DATEDIFF(minute,'20100101',PBXQTime) / 10)*10,'20100101')