New area codes can be assigned in different ways. A region can be split into two parts, one part keeping the old area code and one part getting a new one. This plan is called a split. In an overlay -- the plan chosen for Maryland -- a new area code coexists with the established code, and one result is that all local calls require 10-digit dialing. An overlay also means that neighbors and even phones in the same house can end up with different area codes.
It may be small consolation, but the country has survived phone number changes before. Perhaps the most difficult transition was during the 1960s, when catchy, two-letter prefixes based on the telephone office location (BUtterfield 8, PEnnsylvania 6-5000) were deemed impractical. To provide more usable dialing combinations, the letters were abolished.
That system was called All-Number Calling. In response, a California man named Carl May started the Anti-Digit Dialing League, railing against "the cult of technology" and society's "creeping numberalism." The group -- which had members around the country -- complained that All-Number Calling made dialing mistakes more likely, because seven numbers would be impossible to remember.