Does Your Area Code Fit Here?
According to Wikipedia (WDNL), the 9 is "reserved in case the 3-digit area codes pool is exhausted and has to be augmented to 4 digits." That doesn't make much sense, but whatever.
Some bright person once noticed that some area codes resemble dates. For example, area code 414 looks a little like 4/14 or 4.14 or 4-14. So April 14 (yesterday) is designated as 414 Day (however you want to write it) and is celebrated in the greater Milwaukee, Wisconsin, area.
If you're thinking ahead (not too deeply) on this, you're realizing that some area codes - possibly yours - will never be awarded such a special day because you can't turn said code into a date in the Gregorian system.
For example, just outside of Milwaukee the area code is 262. You could fudge that one and claim it's the equivalent of February 26...26.2...but no one does. And there's obviously no month with 62 days in it (again, in the Gregorian system).
So today is All the Other Area Codes Day on which you can legitimately celebrate your area code if it doesn't lend itself to being a real date on the calendar.
It should be easy for most people to remember this one because it's also Tax Day in the US unless an extension is involved.
Now you have two wonderful reasons to party. Your taxes are done for the year, and your area code might have a special day.