question about Excel time format

I have a .csv file I extracted from our phone system to add up number of minutes each receptionist is on the phone.  the amount of time on the call comes over as 00:03:21(looks to be as general text), which is 3 minutes, 21 seconds on that call.  i have over 3400 entries for just one receptionist.  what i can't figure out is how to get a total sum of this column, like 12:45:47 (12 hours, 45 minutes and 47 seconds in phone calls total for this month for this receptionist).  i have tried all kinds of format changes.  if i type in 00:03:21, it displays 0:03:21 in the column and then the sum works.  and the cell is displayed as an actual time, 12:03:21 AM.  not really what i want but it does appear to add correctly.   even thought i could add a column and custom format it but it just copies the same thing.  it has to be the format of this column but i have searched high and low for a solution.  hopefully i have described my issue with enough detail.  i am using excel 2010.
thanks