Sum number of calls within a specific time frame

I have created a pivot table which properly display the time of day and the number of calls at that time. (There happens to be only one call per minute but in theory there can be multiple calls made in the same minute). I have tried to sum the calls by hour using countif and a variety of other things. Any help would be appreciated! Below is an image of what I am trying to calculate and the sample excel sheet is also attached.

Excel 2010, Table, PivotTable, PowerPivot, PivotChart
With and without formulas.
http://www.mediafire.com/view/gi7ge2tbt4npe49/12_09_13a.xlsx

It looks good but just a question. I don't see any formulas and did you change the number of calls from 1 to random numbers up to 5 just for display purposes? It looks great but I don't follow it without seeing the formulas.

The regular PivotTable does not use formulas,
the PowerPivot PT uses DAX formulas.
PowerPivot is more flexible and more powerful.
Recommended literature:
PowerPivot for Excel 2010 by Russo and Ferrari.
I introduced random numbers for test purposes.