Thank you for your post.
In your table, define a new field of type "Summary". More specifically, pull down the File menu and select "Manage -> Database..." Click on the Fields tab, create a new field "Total CallCost", and to the right, next to "Type: ", select Summary. Click "Create", and a new dialog box appears. Click the first option on the left side, "Total of" and then select the "CallCost" field. Click OK, and you will see a large total. FileMaker Pro is actually calculating the value for the entire found set of records. If you find a subset of records, the value will change. If you place this field in a sub-summary part, the total will be reflected for that group of records.
Following the same steps above, create another Summary field titled "Total Calls" and instead of clicking on "Total of", select the third option "Count of". Again, the same rules apply for the found set, and for each sub-summary.
If you need clarification for any of the above steps, please contact me.