I have a list of phone numbers in column D. I want to count how many of them
begin with a 917 area code excluding duplicates. I then want to subtract that
result from the total number of phone numbers.

I currently use the following formula just to count the number of total
phone numbers excluding dupicates:
=SUMPRODUCT((D2:D123<"")/COUNTIF(D2:D123,D2:D123&""))

Any suggestions on would be greatly appreciated!