NPA-NXX - 240-399

This is the 240-399 subcode (NPA-NXX) prefix page. Follow a prefix to find the number you are looking for. We divide our pages up to make them more user friendly to navigate!

1. Area Codes
2. 240
3. 240-399

The 240-399 subcode mainly covers Washington in Montgomery county. But other numbers maybe included as well.

We have a database of information derived from the public phone records of Maryland state. Many of the numbers in this subcode are Regular Landline registered to Xo Communications. We hear they employ a large number of people in the Maryland office.
Recently there have been an increase in reported calls, we've had over 971777 comments across our systems for the 240-399 subcode.