How can I quickly search a LARGE amount of numbers in the format:

a1 a2 a3 a4 a5 a6...
n1 n6 n11
n2 n7 ...
n3 n8
n4 n9
n5 n10

where a# are three digit area codes and n# are 7 digit phone numbers. The
area code col to be search will be determined and feed from another cell.
Once this formula sees there is an area code it should check the area code
headings for a match then serach that area code col to find a phone number
match if one exist. A simple "Y" or "N" return value would suffice as a
result of the fomula.

Thank You!