jcrawford08,
If the values are negative, it would subtract them, true.
How is that different from what the SUM function does?
If what is needed is total time, ABS could be used to remove any negatives.
(ABS({Table.Field})+ABS({table.Field2})+etc
The OP formula would sum the 1st field (TalkTime) based on the 2nd field (HoldTime) using the condition given in the 3rd field (WorkTime), which most likely does not contain the proper condition string (such as: "monthly" or "for each day", etc) and that doesn't seem to be what the OP really wanted. Or put another way, it groups values in the 1st field (TalkTime) by the 2nd field (HoldTime) and calculates the sum based on the condition defined by the 3rd field (WorkTime). (i could be wrong in my understanding of what the desired end result is, but i have been wrong once already today tho, so the odds are diminished...LOL).
To sum the fields, they should be between brackets like this: sum([{vwEST.TalkTime},{vwEST.HoldTime},{vwEST.WorkTime}])