"Tushar Mehta" wrote...
....
The benefit of the approach should be obvious. The worksheet closely
mimics the stated business problem. The formulas are simple and you
know the results of the intermediate steps -- column of the area code
match and the row of the phone number match, which makes debugging
that much easier. Of course, you can also easily label the
intermediate results by typing in text into an adjacent cell.
....

This is all very nice, but phone number lookups are ideally a database task.
The most sensible way to deal with the business problem is to use the tool
best suited to the task. The OP's task is a form of misuse of spreadsheets.

There's also the matter that the OP's phone number layout is a poor data
structure. Area codes as column headings with local phone numbers below is
much less useful than a single column of area codes and phone numbers
combined, sorted in ascending order. Phone numbers within each area code
would still be grouped, but a single fairly simple MATCH call (separately
entered area code and phone number would need to be concatenated - hopefully
you wouldn't recommend doing that alone in a separate cell) would be able to
determine whether the number exitst.

BTW, Aladin's approach is best, though I might change the custom number
format to "Y";"Y";"N".