|For what you are wanting to do perhaps sorting and sub-totaling would work better or even a pivot table.|
Insert a row (if not already there) in Row A and place column header names to your data such as "Phone number called", "Call Duration" and "Cost of call"
Then select all of your data (Click on A1 or the top left active cell below your column header names, Hold down the Ctrl and Shift keys and hit the End key to select all the data.)
Now go to Data, Sort by the column with the phone numbers.
Now go to Data, Sub-totals and choose a break at each phone number and sum at same.
That should give you a sum of costs associated with each phone number called.
Pivot table: Select all the data as earlier noted and then go to Data, Pivot Table report and use it's wizard.
It may take you couple of tries to get what you want rather than me trying to explain it to you.
I believe Sort and Sub-Totals will get you what you are looking for with relative ease.